Over the last decade, a number of large-scale studies have examined whether attending a charter school can improve students’ performance on standardized tests and other outcomes, compared with attending a traditional public school. Among the key players in this field of research are the Center for Research on Education Outcomes (CREDO) at Stanford University, the public policy research institutes Mathematica Policy Research and the RAND Corporation, and a number of academic researchers from various universities across the country.
Before reviewing the main findings of this research, it is important to understand some basic facts about the methodologies of the most reputable studies in the field.
Studies that are considered methodologically most sound typically study charter school impacts in one of two ways:
It is also important to keep in mind that any research results on charter school impacts on students—from lottery as well as matching studies—can be generalized only to students (and families) who want to attend charters. By definition, charters are schools of choice, and the study samples are therefore limited to students and families who might choose a charter school instead of a traditional public school. This is particularly important to consider if charter applicants systematically differ from students and families who do not apply to charter schools in ways that could affect academic performance. For more information on what is known about whether charters seem to attract more or less prepared students and families, see the Diversity and Inclusion and Families sections.
The main takeaway from studies that have examined charter schools’ impacts on students’ performance on standardized tests is that these impacts vary widely across states, types of students and types of schools, as well as over time. Moreover, the research is continuously evolving as more and better data become available.
Here, we summarize the current state of knowledge of charter schools’ impacts on student achievement. We summarize the field’s key findings, nationally and across states, by student demographics, by types of schools and over time. Our review focuses on the largest and most recent studies as well as selected local studies. While not comprehensive, this review provides a general overview and specific examples of research on charter schools’ impacts on student achievement.
Nationally, there is very little evidence that charter and traditional public schools differ meaningfully in their average impact on students’ standardized test performance. A 2013 study conducted by CREDO (a matching study) drew on data through the 2010–11 school year from 27 states and found that charter schools on average had a small positive impact on students’ reading achievement but no differential impact on students’ math achievement.2 A 2014 meta-analysis of the literature on charter school effects, by researchers with the Center on Reinventing Public Education — a research and analysis organization associated with the University of Washington Bothell that focuses on “innovative schools of choice” and works to “develop, test, and support evidence-based solutions to create new possibilities for the parents, educators, and public officials who strive to improve America’s schools”—reported no significant impacts on reading scores and small positive impacts on math scores.3
In 2017, CREDO published an update to their 2013 study, which examined charter schools across 24 states, New York City and Washington, D.C. The study (a matching study) looked at the effects of charter schools on student growth, as did their previous report, but it also included two new analyses. First, it examined the relationship between student growth and type of charter school operator. The study defines four types of charter school operators: independent or “non-network” charter schools; charter schools managed by organizations that operate multiple schools; “vendor-operated schools,” or charter schools operated by a vendor that provides services to schools without holding those schools’ charters; and what CREDO calls “Hybrid schools.” Hybrid schools, which constitute only 1 percent of all charter schools, combine some elements of a school operated by a charter management organization and some elements of a school operated by a vendor. Some of the organizations that operate multiple charter schools are nonprofit and some are for-profit. CREDO’s second new analysis examined the relationship between student growth and profit status of charter school operators.4 For more information on regulatory and operational variations, see the Charter School Operators section.
The 2017 CREDO study found in general that students who attended any type of charter school showed significant gains in reading compared with their traditional public school counterparts. For example, students who attended a vendor-operated charter school saw approximately 11 additional days of reading, students who attended a charter school managed by an organization that operates multiple schools saw approximately 17 additional days of reading and students who attended a Hybrid charter school saw an equivalent of 46 additional days of reading. However, the only students who showed significant growth in math compared with their traditional public school counterparts were students who attended a charter school managed by an organization that operates multiple schools—they saw an equivalent of 17 additional days of math—and students who attended Hybrid schools—who saw an equivalent of an additional 51 days of math. Students who attended charter schools managed by nonprofit organizations showed significant gains in math and reading compared with their traditional public school counterparts. Students who attended charter schools managed by for-profit organizations showed math growth that was significantly weaker than that of their traditional public school counterparts and showed no difference in reading growth.5
However, there are many different kinds of charter schools, many different types of students and wide variation in states’ charter school laws and hence significantly different regulatory contexts in which charter schools operate. Considering these variations, research findings become more nuanced and more meaningful:
In some states charter schools have had positive impacts on student learning, in other states they have had negative impacts, while in still others charters have had no differential impact compared with traditional public schools. For example, the 2013 CREDO research (matching study) used data through 2010–11 and reported that in 16 states, charter schools were associated with greater reading gains compared with traditional public schools. In eight states, they found negative impacts for charter schools, and in three states they found no differences between charter school and traditional public school students’ reading improvement, on average. The differences ranged from charter schools showing reading gains equivalent to 86 more days of learning than in traditional public schools in Rhode Island and Tennessee, to reading gains equivalent to 108 fewer days of learning than in traditional public schools in Nevada.6 For the full list of charter school impacts by state, see pages 52–53 of CREDO’s “National Charter School Study 2013.”
CREDO authors pointed out that the diversity of charter impacts in generally low-performing areas is particularly noteworthy. On the one hand, charter impacts were associated with the equivalent of 101 extra days of math learning in Washington, D.C., and 94 extra days of math learning in New York City. In these cases, one can argue that charters improve educational opportunities in mathematics for students. On the other hand, when charter schools’ impacts are negative in already low-performing states (for example, Nevada), one may argue that they are further limiting educational opportunities for students.
The 2017 CREDO study found that there were differences in academic growth not only between states but also within states, based on the different type of charter school. Six of the 26 states studied showed, on average, stronger growth in math among those who attended charter schools operated by organizations that run multiple schools compared with those who attended traditional public schools.7 There were only two states in which traditional public school students showed stronger growth in math than students from charter schools operated by organizations that run multiple schools. In 13 states, students at charter schools operated by organizations had stronger reading growth than traditional public school students. In only three states did the traditional public school students show stronger reading growth.8
Charter school impacts vary between states
Number of states in which charter school students show stronger, similar or weaker growth compared with traditional public school students
|Weaker Growth||Stronger Growth||
|Charter schools operated by organizations that run multiple schools||6||8||12||13||10||3|
|Vendor-operated charter schools||4||15||3||6||14||2|
|Hybrid charter schools||2||5||1||2||5||1|
Base: Charter schools operated by organizations that run multiple schools = 26; vendor-operated charter schools = 22; Hybrid charter schools = 8.
Source: Center for Research on Education Outcomes (CREDO), “Charter Management Organizations 2017,” Stanford, Calif.: CREDO at Stanford University, 2017.
Lower-income and urban students are most likely to benefit from a charter education. A number of studies that focus on charter schools in large urban districts (for instance, New York City, Boston and Los Angeles) found positive impacts of charters on students’ standardized test score achievement. For example, Caroline Hoxby and colleagues’ evaluation of New York City charter schools (a lottery study; nearly all New York City charter schools are lottery based) analyzed data through 2007–08 and reported positive impacts for charter schools on students’ achievement in English and math. Instead of looking at additional days of learning, this study examined the achievement gap by looking at standardized test scores. The study found that students who attended a charter school from kindergarten through eighth grade closed about 86 percent of the achievement gap in math and 66 percent of the achievement gap in English. The size of these effects increased as students spent more years in charter schools. Specifically, charter school students scored three points higher on the Regents exam—exams that must be passed in order to graduate high school in New York State—for each year spent at a charter school before taking the test.9 Similarly, Atila Abdulkadiroglu and colleagues (a lottery study) analyzed data through 2006–07 and reported positive impacts on English and math achievement among charter middle and high school students in Boston charter schools.10
These single-city studies are highly informative for charter school debates in those respective cities, but their findings are not easily generalizable beyond their specific locations and populations. First, locations vary in their charter school laws and oversight, which in turn may differentially affect charters’ impacts. Second, as charter school students in large urban cities such as New York City, Boston and Los Angeles are predominantly black or Hispanic and living in poverty, these single-city studies cannot tell us whether the impacts are specific to low-income students, minority students, urban schools, a combination or none of these factors.
National studies, such as the 2013 27-state 2013 CREDO study and Mathematica’s 2010 evaluation of fifth through seventh graders in 36 schools across 15 states, can help disentangle some student subgroup and locale impacts.
CREDO (2013, a matching study, with schools across 27 states) analyzed data through 2010–11 and found charter schools’ greatest impacts on the math and reading growth of low-income minority students (low-income is measured as students’ eligibility for free or reduced-price lunch). For example, black students living in poverty and attending charter schools experienced math gains equivalent to 36 extra days of learning, compared with black students living in poverty and attending traditional public schools. The study reported no differential impacts for black charter school students who were not living in poverty. Similarly, CREDO 2013 found positive impacts for low-income Hispanic students, but negative impacts for Hispanic students who were not living in poverty. Impacts on low-income minority students were especially pronounced in urban areas.11
The 2017 CREDO study found similar results. Black students who attended a charter school were significantly stronger in reading and math outcomes compared with black students who attended traditional public schools. The greatest gains were seen in black students attending charter schools operated by organizations that run multiple schools, with math gains equivalent to 34 additional days and 29 additional days of reading. Interestingly, although they did not find an advantage in mathematical learning in black students who attended Hybrid charter schools compared with black students who attended traditional public schools, Hispanic students who attended Hybrid charter schools gained the equivalent of an additional 74 days in math and 63 days in reading compared with Hispanic students who attended traditional public schools. Students living in poverty, English-language learners and special education students who attended Hybrid charter schools also saw significant gains in math and reading compared with their counterparts in traditional public schools.12
Charter effect by population, math and reading
|Charter schools operated by
organizations that run multiple schools
Vendor-operated charter schools
Hybrid charter schools
|Students living in poverty||+||+||=||=||+||+|
|English Language Learners||=||=||=||=||+||+|
Source: Center for Research on Education Outcomes (CREDO), “Charter Management Organizations 2017,” Stanford, Calif.: CREDO at Stanford University, 2017.
A 2010 study conducted by Mathematica Policy Research, with funding by the Institute of Education Sciences at the U.S. Department of Education, found that charter schools located in urban areas or schools that primarily serve low-achieving or low-income students have more positive impacts and are more successful than those in rural areas or ones that serve higher-income or higher-achieving students. The 2010 Mathematica lottery study looked at 36 charter middle schools across 15 states and found that after two years of enrollment in urban charter schools, students saw significant positive achievement in mathematic scores, compared with students in nonurban charter schools who experienced a significant negative impact. However, when student characteristics and school operations, such as student-teacher ratio and length of the school day, are controlled for, the impacts on math achievement were no longer significant, indicating that urban living may have less to do with impacts, while student characteristics and school operations may drive impacts. The study also found that charter schools with higher percentages of low-income or low-achieving students had positive impacts in mathematic achievement and charter schools with lower percentages of low-income or low-achieving students had significant negative impacts.13
Mathematica’s evaluation of charter middle schools in 15 states (a lottery study) examined data through 2007–08 and also found that both students’ backgrounds and the location of the school mattered for achievement outcomes. The study reported small positive impacts for low-income students (those eligible for free or reduced-price lunch) and somewhat larger negative impacts for higher-income students in reading and math. At the same time, the study found that regardless of income, urban charter schools were more likely to have positive impacts on students’ math achievement than nonurban charter schools, which tended to have negative impacts. After conducting further exploratory analyses, the authors noted that urban charter schools’ relative edge could be due to the possibility that their urban comparison schools offer lower-quality alternatives.14
One charter school’s impact can differ greatly from another’s. Some school characteristics have been found to relate to charter impacts. Every charter evaluation study has reported great variation among individual charter schools’ impacts and among different types of charter schools’ impacts. For example, CREDO 2013 (a matching study) analyzed data through 2010–11 and found that the majority of the schools in their study (56 percent) had no greater or lesser impact on their students’ reading gains than did traditional public schools, but 25 percent of the schools in their study improved students’ reading over and above traditional public schools’ impact, while 19 percent diminished students’ reading gains compared with traditional public schools. The same study also found more positive impacts for charters that were elementary or middle schools, but no impacts for charter high schools.15
Similarly, Mathematica studied the impacts of 22 nonprofit organizations that manage multiple charter schools (a matching study). For more information about these organizations, see the Charter School Operators section. Examining data through 2010–11, Mathematica reported differences in impacts that ranged from the highest-impact nonprofit management organization demonstrating three years’ worth of learning gains within a two-year period to the lowest-performing nonprofit management organization showing as little as one year of learning gains in a two-year period. Overall, the study found positive impacts on students’ math and reading scores in 45 percent of the nonprofit management organizations studied, but just as many nonprofit management organizations had negative impacts in either math or reading.16
Charter schools’ impacts can vary between schools even within a nonprofit management organization. For example, studying impacts of one specific nonprofit management organization, the Knowledge Is Power Program (KIPP) (matching and lottery study), Mathematica examined data through 2010–11 and found that while KIPP middle schools had overall positive impacts on student learning in reading and math, some KIPP middle schools had greater impacts than others. Digging further, the study found that KIPP schools with higher percentages of students enrolled in special education relative to the district and KIPP schools that emphasized school-wide behavior management approaches saw higher impacts on math and reading.17
Another study conducted by Mathematica (a lottery study) examined the longitudinal effects of KIPP pre-kindergarten and KIPP early elementary programs. The study followed a cohort of students who were enrolled in KIPP pre-K and students who were not accepted into the program in 2011 and then in 2016 looked at second-grade outcomes among those students who had enrolled in KIPP pre-K and those who were not offered admission to KIPP pre-K. The study found that there were large and significant math impacts of KIPP pre-K and early elementary programs after five years. The study also found some reading impacts among those who enrolled in KIPP pre-K. Specifically, there were long-term significant impacts on the Woodcock-Johnson III (WJ-III) Letter-Word Identification, a standardized test of reading achievement, throughout the five-year study. Although there were initial impacts on reading comprehension, these were no longer significant after five years. The study also found a positive impact after five years on executive function for students who attended both KIPP pre-K and KIPP early elementary as measured by the Woodcock- Johnson III (WJ-IV) Verbal Attention test.18 The WJ-IV Verbal Attention test specifically measures working memory and the ability to follow instructions.
Not only do impacts differ between individual charter schools, but the impacts of charter schools can change over time. In a 2013 study of charter schools in Texas, CREDO (a matching study) found that attending a charter school was equivalent to fewer days of learning in reading and math compared with attending a traditional public school. However, four years later, CREDO’s 2017 study concluded that students who attended a Texas charter school saw a gain of 17 additional days of learning in reading compared with traditional public schools and performed equally well in math. This study does not investigate whether charter schools were performing better or traditional public schools were performing worse over the four-year period of time. But it does show a shift from traditional public schools in Texas offering better reading and math educational opportunities to charter schools in Texas offering better opportunities.19
Such variation raises the question of what aspects of a charter school make it more or less likely to impact students’ learning compared with traditional public schools. While results pertaining to this question are correlational and hence preclude us from making direct and confident attributions about cause, the relationships are suggestive in ways that warrant further study. For example, although research cannot show with certainty that the following charter school characteristics are always directly related to positive impacts, studies have shown that in some cases positive impacts may be correlated with charter schools that provide longer school days—when extended hours are spent on core academics rather than noncore academics; more time devoted to core academic tasks each day; a longer school year; and mission statements that emphasize academic performance and high expectations. Some studies have also suggested positive impacts may be correlated with charter schools that provide frequent tutoring for students in small groups and frequent feedback and coaching for teachers—specifically, observations and feedback by coaches, principals and other administrators, along with reviews of lesson plans. Some studies have also indicated that positive impacts may be correlated with charter schools that have comprehensive school-wide disciplinary systems with rewards and sanctions and that use data from frequent assessments to inform instruction.20 However, while characteristics such as longer school days are easier to define, others are more difficult to define, implement with fidelity and compare across multiple schools, such as school-wide disciplinary systems or the use of data to inform instruction. It is therefore important for future research to explore which specific practices are most effective within these less well-defined charter school characteristics that may be correlated with positive impacts.
For more information about the research on these and other practices, see the Innovation section.
There is comparatively little rigorous research comparing charter schools with traditional public schools on measures of academic outcomes other than standardized test scores, such as indicators of academic engagement and motivation, high school completion, college matriculation, graduation and so on. These tend to be long-term outcomes that cannot be measured until several years after students entered a charter school. Moreover, much of this information is not collected in the same comprehensive ways as standardized test scores.
However, a growing number of studies have looked at additional measures of academic engagement and success. Their results typically mirrored what they reported on charters’ impacts on standardized test scores.
For example, Mathematica researchers’ 15-state study of charter school fifth through seventh graders (lottery study)—a study that examined data through 2007–08 and found no differential impacts for charters overall—reported no evidence that charter school students had better school attendance or grade promotion than their peers in traditional public schools.21
However, studying charter schools’ impacts in New York City with data through 2007–08, Caroline Hoxby and colleagues (lottery study) not only found positive charter impacts on math and reading scores but also reported that the longer students stayed in charter schools, the higher they scored on the New York State high school Regents examinations and the more likely they were to earn a New York State Regents diploma. Similarly, Joshua Angrist and colleagues’ 2013 lottery-based evaluation of Boston charter schools reported positive impacts for charter schools not only on students’ standardized test scores but also on indicators of college preparedness, including SAT scores and students’ likelihood to enroll in a four-year college.22 Will Dobbie and Roland Fryer Jr., too, found in their 2012 survey of former students that winning a lottery-based place at Promise Academy in Harlem increased students’ college enrollment rate and especially their likelihood to enroll in a four-year higher education institution.23
Evaluating charters in eight locations (matching study), Ron Zimmer, Brian Gill and colleagues reported positive impacts of charter school education on academic outcomes other than standardized test scores, using data through 2006–07. In a sample of charter middle school students in Florida and Chicago, students who transferred into a charter high school were more likely to graduate from high school and more likely to attend college than those charter middle school students who did not transfer into a charter high school.24
Mathematica researchers reported that students who were offered a lottery-based place at KIPP middle schools not only performed better on standardized math and reading tests than students who did not win a seat in a KIPP school but also reported doing more homework and being more satisfied with their school. At the same time, the study found no difference between KIPP lottery winners and non-winners on such measures as academic engagement and effort and educational aspirations (all self-reported by students).25
A matching study published in 2017 that examined outcomes of Chicago’s charter high schools found that although charter school students on average had better attendance than Chicago traditional public school students, they had similar study habits and grit and graduated high school at comparable rates. However, charter high school students in Chicago saw better postsecondary outcomes. Forty-five percent of students who entered a charter high school in 2008, 2009 or 2010 enrolled in a four-year college upon high school graduation, compared with only 26 percent of students who attended Chicago’s traditional public schools. The study also found that charter high school students, as opposed to traditional public high school students, reported they were more engaged in planning their future and felt their schools were more likely to promote college readiness.26
Again, there is significant variation in the extent to which charter schools impact students’ academic engagement and success. Across six nonprofit management organizations, Mathematica (matching study) found no overall impact on high school graduation but substantial variation among nonprofit management organizations, ranging from one that increased students’ probability of graduating by 23 percent to another that reduced students’ likelihood of graduating high school by 22 percent. Similarly, the study that examined Chicago’s charter high schools found great variation in student outcomes among different schools. Although overall charter school students outperformed traditional Chicago public school students, there were some charter schools whose performance was similar to that of the lowest-performing traditional public schools.27
There is hardly any research so far that estimates how a charter school education shapes students’ future employment trajectories and income. One exception is a matching study by Kevin Booker and colleagues. Leveraging long-term student tracking data from Florida through 2006–07, this study matched charter high school students who had also attended charter middle schools with charter middle school students who had not attended charter high schools and found that in their early to mid-20s, former charter high school students had significantly higher earnings.28
However, in a 2016 study (matching study) Will Dobbie and Roland Fryer Jr. looked at administrative data from Texas to estimate the impacts of charter schools on earnings. The study examined the effects of “No Excuses” charter schools—those that have comparatively strict disciplinary codes, extended days, longer school years, uniform requirements and regimented behavioral expectations—compared with charter schools that are not No Excuses. While the study found that No Excuses charter schools had significant impacts on state test scores, high school graduation and college enrollment, it did not find that attending No Excuses charter schools in Texas impacted earnings later in life. Students who attended other charter schools showed a decrease in earnings.29
The mission of public education extends beyond academic learning to include the preparation of students to be engaged citizens. An important research question is therefore how successful charter schools are in developing students’ civic knowledge, skills and attitudes, in both the short and the long term.
Civic engagement outcomes are again more difficult to measure and track than students’ standardized test scores. Hence there is so far little research on this issue. In one early matching study, Jack Buckley and Mark Schneider reported that charter school students who were surveyed in 2003 reported more civic skills training and community participation but were no different in their endorsement of civil liberties from their peers in traditional public schools.30
Recent studies have not included civic engagement outcomes, even though a number of charter school networks focus explicitly on civic education.
The literature on charters’ impacts on behavioral and health-related outcomes is limited to small-scale studies that focus on specific charter schools, and their findings are mixed.
Will Dobbie and Roland Fryer Jr. analyzed data through 2012 and reported a decline in teenage pregnancy for females and a decline in incarceration rates among males who won a place at Promise Academy in Harlem, compared with their peers who did not win a lottery-based seat at the school. However, the study found impacts neither on behaviors such as alcohol or drug use nor on health outcomes. Information on these outcomes was collected through surveys with students.31
Mathematica’s evaluation of KIPP middle schools (a lottery study) utilized data through 2010–11 and found that KIPP lottery winners were also more likely to say they argued with their parents, lost their temper, lied or gave teachers a hard time than students who applied to KIPP but did not win a place—results the authors suggest could reflect true differences in behavior or differences in students’ likelihood to honestly report such behavior. At the same time, Mathematica found no difference in how KIPP lottery winner parents and parents whose children did not win a lottery-based seat described their children’s behavior outside of school and behavioral problems.32
In a 2015 Mathematica report (a lottery study) that builds upon Mathematica’s 2010 and 2013 evaluations of KIPP schools funded by the U.S. Department of Education, there was no evidence that KIPP charter schools affect behavior at the elementary or middle school level. The study used student and parent surveys to measure behavior defined as undesirable behavior, positive behavior, illegal activities, peer pressure, frequency of school disciplinary action and parental concern.33
It is generally acknowledged that a lot more research, and much more data, is needed to understand if, how and when charter schools shape children’s academic and nonacademic outcomes.
To fully understand charter schools’ impact on all students’ achievement, it is important to consider whether the existence and expansion of charter schools affect academic and nonacademic outcomes of students in nearby traditional public schools.
Advocates have argued that charter schools carry the potential to increase competition in the education market and thus encourage traditional public schools to do more to improve student performance. Proponents have also often pointed out that charter school innovations could spread to traditional public schools, an issue that our Innovation section discusses in more detail. Skeptics have pointed out that the existence of charter schools could negatively impact the education and performance of students in nearby traditional public schools by taking financial resources away from those public schools and by attracting the most motivated and engaged families (“cream skimming”). For more information on these issues, see the Diversity and Inclusion and Finances sections.
Studies have measured charter schools’ “pressure” on traditional public schools by a) the proportion of public school students in a given district who are enrolled in charter schools; or b) the number of charter schools located within a certain radius of a traditional public school; or c) the percentage of students a school has lost to charter schools each year. These studies use longitudinal student test score data to examine whether traditional public school students’ performance changed with increasing pressure from charter schools.
The results of these studies are mixed and vary notably across location. Moreover, whenever impacts were found, they have typically been small.
Some studies have found no evidence that charter school competition affected the performance of students in nearby traditional public schools. For example, Ron Zimmer and Richard Buddin, using data through the 2001–02 school year, found no evidence that competition from charters impacted the test score performance of traditional public school students in California.34 Similarly, Robert Bifulco and Helen Ladd, also using data through the 2001–02 school year, found no evidence for such impacts in North Carolina.35 Ron Zimmer, Brian Gill and colleagues found no impact in seven of the eight states and districts they studied, using data through the 2007–08 school year.36 Analyzing spring 2002 data from a national student sample, Tomeka Davis, too, found no evidence that charter school competition affected students’ achievement in traditional public schools.37
Some studies have reported findings that showed positive impacts of charter school competition on the standardized test scores of students in nearby traditional public schools. For example, Kevin Booker and colleagues analyzed data from Texas through the 2003–04 school year and found that students’ performance in traditional public schools improved as charter schools came to their districts. They found particular improvement among low-income and African-American and Hispanic students in traditional public schools.38 Using data through the 2004–05 school year and a different statistical method from that of Bifulco and Ladd’s study cited above, Yusuke Jinnai found small positive impacts in North Carolina.39 Small positive impacts have also been reported for Florida.40
Marcus Winters found some evidence in New York City that traditional public school students’ scores improved slightly as charter school competition grew, analyzing data through the 2008–09 school year.41 Sarah Cordes also examined the effects of charter schools on public traditional schools in New York City and found similar results. Cordes examined charter school student and traditional public school student data in community school districts that have charter schools, along with colocation charter and traditional public schools, from the 1996–97 through the 2009–10 school years in grades three through five. Starting in 2007, all charter schools in New York City had to offer admission preference to those who lived in the same community school district as the charter school; thus, the effects of the charter schools may affect the community schools the most. Cordes found that the presence of charter schools significantly increased language and math performance and significantly decreased grade retention for traditional public school students within the same community districts. Cordes also found that charter schools in colocations showed the largest impacts on the traditional public schools.42
However, Yongmei Ni, using data through 2003–04 from Michigan, reported small negative impacts on traditional public school students’ tests that increased with the number of years traditional public schools experienced charter competition.43 Based on data through 2004–05, Scott Imberman reported small negative impacts on student achievement in one large southwestern district but positive impacts on middle and high school students’ discipline.44
Again, more research is needed regarding the effects of charter schools on the achievement of students in nearby traditional public schools. Existing studies are limited to specific areas and may not be generalizable nationally. They have looked almost exclusively at standardized test scores—an important but limited outcome—and the most recent data they consider is from 2009. As the number of charter schools has increased nationwide, forthcoming studies can be expected to leverage more recent data and thus estimate impacts of increased charter school competition on traditional public schools.