Scott Alexander critically examines studies on preschool effects, finding mixed and inconsistent evidence for long-term benefits. Longer summary

Scott Alexander reviews multiple studies on the long-term effects of preschool programs like Head Start. While early studies showed fade-out of test score gains, some found lasting benefits in adult outcomes. However, Scott finds inconsistencies between studies in which subgroups benefit and on which outcomes. He also notes concerns about potential p-hacking and researcher degrees of freedom. Ultimately, Scott concludes that the evidence is mixed - it permits believing preschool has small positive effects, but does not force that conclusion. He estimates 60% odds preschool helps in ways suggested by the studies, 40% odds it's useless. Shorter summary

Scott Alexander admits he was wrong about preschool programs like Head Start, discussing new evidence of their long-term benefits and considering the implications for understanding environmental effects and policy. Longer summary

Scott Alexander reflects on his previous skepticism about the effectiveness of preschool programs like Head Start, admitting he was wrong based on new evidence. The post discusses research showing that while preschool doesn't improve academic skills or IQ, it does lead to better long-term life outcomes such as staying in school longer, getting better jobs, and committing less crime. Scott speculates that these benefits might stem from social factors like freeing up parents' time or exposing children to different environments. He also grapples with how this conflicts with studies showing little impact of shared environment on outcomes, and considers implications for policy support of universal childcare or pre-K programs. Shorter summary