Instruction in peer assessment of complex task performance may cause high cognitive load, impairing learning. A stepwise instructional strategy aimed at reducing cognitive load was investigated by comparing it with a combined instructional strategy in an experiment with 128 secondary school students (mean age 14.0 years; 45.2% male) with the between-subjects factor instruction (stepwise, combined). In the stepwise condition, study tasks in Phase 1 were domain-specific and study tasks in Phase 2 had both domain-specific and peer assessment components. In the combined condition, these two components were present in all tasks in both phases. Final performance (i.e. speed and accuracy in domain-specific skills and peer assessment skills) showed no significant differences, but performance improved more from Phase 1 to Phase 2 in the stepwise condition than in the combined condition. The results suggest that, with complex study tasks, it might be beneficial to teach domain-specific skills before peer assessment skills. (Contains 2 tables and 5 figures.)