We utilize random assignment of students into classrooms in China middle schools to study the mechanisms behind the spillover of peer parental education on student achievement. Analyzing the China Education Panel Survey, we find a causal relationship between classmates' maternal education and student test score. In addition to the conventional peer effect and teacher response channel, we identify mother adjustment of parenting style as another important mediating factor. We provide suggestive evidence about the existence of mother's network, which facilitates the change in parenting style. We also find that the spillover of peer maternal education on non-repeaters and non-migrant students is stronger, primarily driven by higher parental investment on time.