Peer feedback is frequently implemented with academic writing tasks in higher education. However, a quantitative synthesis is still lacking for the impact that peer feedback has on students' writing performance. The current study conveyed two types of observations. First, regarding the impact of peer feedback on writing performance, this study synthesized the results of 24 quantitative studies reporting on higher education students' academic writing performance after peer feedback. Engagement in peer feedback resulted in larger writing improvements compared to (no-feedback) controls (g = 0.91 [0.41, 1.42]) and compared to self-assessment (g = 0.33 [0.01, 0.64]). Peer feedback and teacher feedback resulted in similar writing improvements (g = 0.46 [-0.44, 1.36]). The nature of the peer feedback significantly moderated the impact that peer feedback had on students' writing improvement, whereas only a theoretically plausible, though non-significant moderating pattern was found for the number of peers that students engaged with. Second, this study shows that the number of well-controlled studies into the effects of peer feedback on writing is still low, indicating the need for more quantitative, methodologically sound research in this field. Findings and implications are discussed both for higher education teaching practice and future research approaches and directions.