Should-Read: Elizabeth U. Cascio: Does Universal Preschool Hit the Target?: Program Access and Preschool Impacts: "This paper takes advantage of age-eligibility rules to construct an instrument for prekindergarten (pre-K) attendance...
...in survey data where the mediating influence of program access can be directly assessed... exploit[ing] the relatively large difference in pre-K attendance rates between 4 year olds in adjacent kindergarten entry cohorts in states with robust state-funded pre-K programs. This approach reveals a substantial positive effect of attending pre-K on cognitive test scores at age 4, but only for low-income children enrolled in universal programs.
Both universal and targeted programs displace enrollment in other center-based care, and differences in state standards cannot explain the higher impacts of universal programs for low-income children. Together, these findings suggest that universal programs offer a relatively high-quality learning experience for low-income 4 year olds not reflected in the quality metrics frequently targeted by policymakers...