We investigated whether personality moderates group influence of classmates on academic achievement and whether these so-called context effects can be attributed to peer pressure. The sample consisted of 2498 students in their first year of Dutch secondary education. The data were analyzed by a two-level (students within classes) analysis, separately for boys (n=1033, in 92 classes) and girls (n=1465, in 119 classes). For both sexes, we found a context effect on Dutch language achievement but not on mathematics achievement. Emotional Stability appeared a moderator of this context effect but for girls only. The results suggest further that peer pressure is not a likely mechanism of group influence of classmates on academic achievement.