Pre-kindergarten (pre-k) is thought to have both direct and indirect effects on children's outcomes in early elementary school. Direct pre-k effects consistently include moderate to large gains in academic skills and sometimes include increases in problem behaviors that affect acquisition of skills in school. Indirect pre-k effects assume that having more pre-k attenders in classrooms motivates teachers to provide more challenging instruction and provide children with more academically skilled, but perhaps behaviorally challenged peers with whom they interact. To date, these indirect effects have not been carefully examined. This study used a district-wide cohort study of a pre-k program (n = 2572 children, 482 kindergarten classrooms) to examine whether the proportion of children in kindergarten classrooms with pre-k experience related to gains in children's academic, executive function, and social skills during kindergarten. Results indicated that schools with more pre-k attenders served more children from low-income families and children of color. The quality of instruction in classrooms with more pre-k attenders was rated as slightly higher in terms of instructional support and focus on abstract learning when school composition was not considered. Teachers reported less focus on teachers-parent coordination of home learning in classrooms with more pre-k attenders. Children with more classmates who attended pre-k, regardless of their own pre-k attendance histories, showed slightly larger gains in vocabulary and inhibitory control skills but also showed smaller increases in ability to manage frustration. When taken together, findings may indicate that peers influence young children's verbal and social skills, but do not support speculation that increasing pre-k exposure would improve reading or math skills overall or lead to more externalizing behavior problems.