Friends in early adolescence play a significant role in students' lives, potentially influencing their academic performance. A multi-group stochastic actor-oriented model was employed to examine the effects of social selection and peer influence through friendship ties on Czech language grades and reading literacy among lower-secondary students, controlling for students' SES, gender, and network structure. The sample comprised 276 sixth-grade students across twelve classrooms, measured at two time points with an interval of seven months. No evidence of selection or influence in terms of grades and literacy was found. However, effects of gender and SES assortativity were observed. The findings are discussed in relation to potential publication bias in the existing literature, and implications for future research are outlined.