Abstract: Using the random class assignment sample from the China Education Panel Survey( CEPS) , this paper analyzes the spillover effects of classmates'preschool enrollment rates on the academic achievement and mental health of middle school students. 'The empirical results show that the classmates’ preschool enrollment rates have significant positive spill.over elfects on both academic achievement and mental health. Peers who received preschool education improved the classroom atmosphere, enhanced students'interpersonal relationships, and promoted students’ learning behaviors. For academicperformance, the spillover elfects of classmates’ preschool enrollment rates are primarily driven by peers with longer durations of prechool education, and are more pronounced among seventh and eighth graders. For mental health, the spilloverelfects of classmates’preschool enrollment rates are concentrated among disadvantaged students, with particularly strong improvements observed in eighth and ninth graders.

Key words: preschool education, spillover effects, academic achievement, mental health