Do preschool classmates determine whether early education gains persist?
Core argument: Holding class size constant, one additional preschool-program classmate raises preschool children's cognitive skills by roughly 0.10 SD, linking the fade-out effect to the share of classroom peers assigned preschool access.
We first randomly assign preschool access to children, and then partner with the local school district to randomly assign the same children to classmates throughout elementary school. We find that the fade-out effect is critically-linked to the share of classroom peers assigned to preschool access. Preschool children benefit greatly from having other Preschool children in the same class. Holding constant the total number of students in class, one additional Preschool classmate significantly increases cognitive skills by roughly 0.10 SD. Immediately after program implementation, Preschool CHECC children had 0.13 standard deviations higher cognitive skills than control children (leftmost bar of Figure 3). Second, turning to the impacts of Preschool on cognitive skills during elementary school, the two rightmost bars of Figure 3 reveal that during grades 2-5, when Preschool children are exposed to many Preschool classmates, they have roughly 0.26 standard deviations higher cognitive skills than control children.



