In this study the relationship between domain-specific skills and peer assessment skills as a function of task complexity is investigated. We hypothesised that peer assessment skills were superposed on domain-specific skills and will therefore suffer more when higher cognitive load is induced by increased task complexity. In a mixed factorial design with the between-subjects factor task complexity (simple, n = 51; complex, n = 59) and within-subjects factor task type (domain-specific, peer assessment), secondary school students studied four integrated study tasks, requiring them to learn a domain-specific skill (i.e. identifying the six steps of scientific research) and to learn how to assess a fictitious peer performing the same skill. Additionally, the students performed two domain-specific test tasks and two peer assessment test tasks. The interaction effect found on test performance supports our hypothesis. Implications for the teaching and learning of peer assessment skills are discussed. (Contains 5 figures and 2 tables.)