This publication summarizes an academic review paper on preschool effectiveness, "Lottery Evidence on the Impact of Preschool in the United States: A Review and Meta-Analysis" by Jesse Bruhn and Emily Emick. The 44 papers summarized fall into three categories: studies of three model preschool programs begun in the 1960s known as "demonstration programs," studies of four modern-day preschool programs, and studies of 14 experiments comparing preschool characteristics. The included papers use lottery-based designs to determine the causal impacts of preschool. When preschools have more interested students than seats, they use lotteries to determine who gets an offer. This context allows for apples-to-apples comparisons between the outcomes of successful and unsuccessful applicants.