This study applied Simulation Investigation for Empirical Network Analysis to disentangle friendship selection and influence regarding the academic achievement of Chinese adolescents in a 3-year longitudinal study of 880 middle school students (400 girls, Year 1 mean age = 13.33) and 525 high school students (284 girls, mean age = 16.45). Both peer selection and influence effects were obtained. Chinese adolescents preferred friendships with similarly achieving or higher achieving peers but avoided friendships with lower achieving peers. They increased achievement when they befriended high-achieving peers but decreased achievement when they befriended low-achieving peers. Influence but not selection was stronger for middle school students than for high school students. The results may be a function of the importance of academic success for Chinese students.