Harlem Children's Zone — Promise Academy Charter Schools
Harvard University / Harlem Children's Zone · New York City, USA · 2004
Summary
The Harlem Children's Zone experiment addressed one of the most politically charged questions in American education: can the achievement gap between Black and white students be closed? The lottery comparison found that Promise Academy middle school students closed the gap in math virtually entirely — a finding without precedent in the literature. But the study produced an equally important secondary finding: the community wraparound programs that made HCZ famous — the parenting classes, health services, and neighborhood programming across 97 blocks — appeared to contribute little independently. The school itself was doing the work. This finding shifted policy discussions from comprehensive community investment (HCZ's stated model) to school quality (what the evidence actually supported). The most effective elements appeared to be extended learning time, high teacher expectations, frequent assessment, and data-driven instruction — features common to other high-performing charter schools, not unique to the community-embedded model. It remains one of the most instructive cases for distinguishing between program theory and program mechanism.
Research question
"Does attending a high-intensity charter school embedded in a comprehensive community support network eliminate the Black-white achievement gap?"
Methodology
Intervention
Harlem Children's Zone operates comprehensive programming across 97 blocks of Central Harlem: parenting classes, after-school programs, community health, social services. The Promise Academy charter schools within HCZ offer extended school day/year, intensive teacher coaching, wrap-around social services. Schools are oversubscribed; researchers used lottery for entry as natural experiment.
Assignment
Lottery-based natural experiment; Dobbie & Fryer (2011) identified lottery offers as instrument; compared lottery winners to lottery losers in same cohort
Sample size
Approximately 900 lottery applicants analyzed; school serves ~1,400 students K-12
Primary outcome
Math and English achievement (standardized test scores) at grades 4 and 8; college attendance
Effect estimate
Middle school HCZ: math scores closed Black-white achievement gap entirely (+.23 SD effect per year); English/ELA: smaller but significant gains (+.047 SD/year); elementary school: similar math gains. Key finding: lottery analysis suggested community programs outside school showed limited independent effect — it was the school that drove gains
Decision
Promise Academy model cited by Obama administration in 'Promise Neighborhoods' federal initiative ($500M allocated for HCZ-inspired programs in 20+ cities); study prompted significant debate about which component of comprehensive programs drives effects; Dobbie-Fryer methodology became standard for evaluating charter school lotteries; subsequent research found that teacher quality and extended time, not community programs per se, explained most gains
Result
Positive
Middle school HCZ: math scores closed Black-white achievement gap entirely (+.23 SD effect per year); English/ELA: smaller but significant gains (+.047 SD/year); elementary school: similar math gains. Key finding: lottery analysis suggested community programs outside school showed limited independent effect — it was the school that drove gains
Evidence strength
Strong
Randomized controlled trial with large sample.
Replication status
Partially replicated
Institution
Harvard University / Harlem Children's Zone
Location
New York City, USA
Year
2004
Policy area
Education
Mechanism
Human capital