Peer assessment is increasingly being used as a pedagogical tool in classrooms. Participating in peer assessment may enhance student learning in both cognitive and non-cognitive aspects. In this study, we focused on non-cognitive aspects by performing a meta-analysis to synthesize the effect of peer assessment on students' non-cognitive learning outcomes. After a systematic search, we included 43 effect sizes from 19 studies, which mostly involved learning strategies and academic mind-sets as non-cognitive outcomes. Using a random effects model, we found that students who had participated in peer assessment showed a 0.289 standard deviation unit improvement in non-cognitive outcomes as compared to students who had not participated in peer assessment. Further, we found that the effect of peer assessment on non-cognitive outcomes was significantly larger when both scores and comments were provided to students or when assessors and assessees were matched at random. Our findings can be used as a basis for further investigation into how best to use peer assessment as a learning tool, especially to promote non-cognitive development.