Abstract

Abstract Background The achievement composition effect (ACE) posits that students' academic performance is influenced by the collective achievement level of their classmates. While ACE has been demonstrated across various learning domains, its role in second language (L2) learning and motivational moderators of this effect remain underexplored. Aims This longitudinal study examines ACE in the context of L2 learning, with a particular focus on the moderating roles of students' intrinsic motivation and engagement. Methods A sample of 766 secondary school L2 learners from 30 classrooms was analysed using linear mixed‐effects models to investigate the relationship between students' relative achievement at Time 1 and their subsequent achievement at Time 2, as well as the moderating effects of intrinsic motivation (to know, to accomplish and to experience stimulation) and engagement (behavioural and emotional). Results Results indicate that students' relative achievement significantly predicts subsequent achievement, supporting the presence of ACE in L2 classrooms. Moreover, intrinsic motivation to experience stimulation, behavioural engagement and emotional engagement significantly moderated this relationship in that ACE was stronger among students with higher levels of these motivational and engagement factors. Conclusion The findings highlight the interplay between peer achievement and individual motivational factors in shaping learning outcomes. The discussion situates these results within the broader literature on peer influence, motivation and engagement, exploring their theoretical and practical implications for L2 learning. The study underscores the importance of considering social, motivational, affective and behavioural factors in understanding and fostering optimal L2 learning environments.