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This paper empirically evaluates the cost-effectiveness of Head Start, the largest earlychildhood education program in the United States. Using data from the randomized Head Start Impact Study (HSIS), we show that Head Start draws a substantial share of its participants from competing preschool programs that receive public funds. This both attenuates measured experimental impacts on test scores and reduces the program's net social costs. A cost-benefit analysis demonstrates that accounting for the public savings associated with reduced enrollment in other subsidized preschools can reverse negative assessments of the program's social rate of return. Estimates from a semi-parametric selection model indicate that Head Start is about as effective at raising test scores as competing preschools and that its impacts are greater on children from families unlikely to participate in the program. Efforts to expand Head Start to new populations are therefore likely to boost the program's social rate of return, provided that the proposed technology for increasing enrollment is not too costly.

Who Benefits from KIPP? * The nation's largest charter management organization is the Knowledge is Power Program (KIPP). KIPP schools are emblematic of the No Excuses approach to public education, a highly standardized and widely replicated charter model that features a long school day, an extended school year, selective teacher hiring, strict behavior norms, and a focus on traditional reading and math skills. No Excuses charter schools are sometimes said to focus on relatively motivated high achievers at the expense of students who are most diffiult to teach, including limited English proficiency (LEP) and special education (SPED) students, as well as students with low baseline achievement levels. We use applicant lotteries to evaluate the impact of KIPP Academy Lynn, a KIPP school in Lynn, Massachusetts that typifies the KIPP approach. Our analysis focuses on special needs students that may be underserved. The results show average achievement gains of 0.36 standard deviations in math and 0.12 standard deviations in reading for each year spent at KIPP Lynn, with the largest gains coming from the LEP, SPED, and low-achievement groups. The average reading gains are driven almost completely by SPED and LEP students, whose reading scores rise by roughly 0.35 standard deviations for each year spent at KIPP Lynn. JEL Classification:I21, I24, I28

Estimates using admissions lotteries suggest that urban charter schools boost student achievement, while charter schools in other settings do not. Using the largest available sample of lotteried applicants to charter schools, we explore student-level and school-level explanations for this difference in Massachusetts. In an econometric framework that isolates sources of charter effect heterogeneity, we show that urban charter schools boost achievement well beyond that of urban public school students, while non-urban charters reduce achievement from a higher baseline. Student demographics explain some of these gains since urban charters are most effective for non-whites and low-baseline achievers. At the same time, non-urban charter schools are uniformly ineffective. Our estimates also reveal important school-level heterogeneity within the urban charter sample. A non-lottery analysis suggests that urban charters with binding, well-documented admissions lotteries generate larger score gains than under-subscribed urban charter schools with poor lottery records. Finally, we link charter impacts to school characteristics such as peer composition, length of school day, and school philosophy. The relative effectiveness of urban lottery-sample charters is accounted for by these schools' embrace of the No Excuses approach to urban education. I IntroductionA growing body of evidence suggests that urban charter schools have the potential to generate impressive achievement gains, especially for minority students living in high-poverty areas. In a series of studies using admissions lotteries to identify causal effects, we looked at the impact of charter attendance in Boston and at a KIPP school in Lynn, Massachusetts (Abdulkadiroglu et al., 2009(Abdulkadiroglu et al., , 2011Angrist et al., 2010aAngrist et al., , 2010b This paper documents the magnitude of treatment effect heterogeneity in a large sample of Massachusetts charter schools and develops a framework for interpreting this heterogeneity using both student-and school-level explanatory variables. We begin with a semiparametric investigation of potential outcomes that assigns a role to variation in no-treatment counterfactuals and 1 Other studies documenting heterogeneity in the effects of charter schools include Hoxby (2004), Zimmer et al. (2009), andImberman (2011). The Imberman study reports that urban charters born as charters have large effects on discipline and attendance, while converted schools do not. 2 A focus on differences between urban and non-urban schools also appears in research on Catholic schools. Evans and Schwab (1995) and Neal (1997) show that Catholic school attendance leads to increases in high school graduation and college attendance for cohorts graduating in the early 1980s. Both studies find larger benefits for black students and for students in urban settings. Grogger et al. (2000) and Altonji et al. (2005) report similar results on Catholic schooling for more recent cohorts.1 to charter applicants' demographic characteristics and bas...