Over-subscribed urban charter schools that admit students by lottery have produced the largest improvement in student achievement.
Comparisons of those who did and did not win charter school admissions lotteries in Massachusetts suggest that urban charter schools boost student achievement. In Explaining Charter School Effectiveness (NBER Working Paper No. 17332), Joshua Angrist, Parag Pathak, and Christopher Walters find that student demographics are related to the extent of this improvement: urban charter schools are most effective for non-whites and low-baseline achievers. They also find that while over-subscribed urban charter schools that admit students by lottery have produced the largest improvement in student achievement, non-urban charter schools are uniformly ineffective in raising measured achievement.
This research uses data on students who attended any of 32 Massachusetts charter schools at any time between the 2001-2 and 2009-10 school years. The authors match school records with test scores and administrative data, including demographic variables such as race, gender, and poverty status, as well as information on school policies, teaching staff, and hours spent in school. Overall their results show that middle school charter lottery winners outscored lottery losers somewhat in English and more significantly in math. High school lottery winners outscored lottery losers about equally in English and math.
Massachusetts' urban charter school students are drawn from a population in which middle school students generally score below the average on state-wide math and English tests. The authors estimate that one year in an urban lottery charter middle school boosts scores dramatically, by 0.34 standard deviations in math and 0.14 standard deviations in English. In contrast, non-urban charter schools appear to degrade performance. Although, as the authors note, "most non-urban students do reasonably well in any case," the causal effect of a year of non-urban charter attendance is a substantial reduction in achievement in all levels and subjects, on the order of 0.16 standard deviations in middle school with almost a quarter of a standard deviation decline in high school math.
The researchers conclude that the relative effectiveness of urban lottery charter schools can be explained by over-subscribed schools' embrace of the No Excuses approach to education.