This lecture explores the impact and effectiveness of peer tutoring, discussing evidence from various studies and meta-analyses. It covers the positive effects of peer tutoring on both the tutored and the tutor, as well as the reasons why peer learning is often successful, such as the 'Curse of Knowledge' effect and the constructive activity effect for tutors. The lecture also delves into a study involving Dutch students solving complex biology problems individually and in groups, highlighting the differences in post-test results.