Purpose: Peer review is one teaching activity that is gaining ground in academic writing training. Studies have addressed the variety of benefits involved and students are able to identify peer review's positive aspects. However, it is still unknown whether the impact peer review has on texts is aligned with what students believe. This research investigates the correlation between students' perceived benefits of peer review and the impact this practice has on their texts. Design: This mixed-methods study involves 45 freshmen attending a compulsory course on communicative competence in the largest university in the Basque Country (Spain). The students created two versions of the introduction of a scientific paper in their mother tongue: one before and one after receiving peers' feedback. They also answered a questionnaire about their beliefs regarding the efficacy of this activity. Findings: Results show that, overall, peer review has a significant effect on students' academic writing. Specifically, the effect is relevant to the use of resources and structure. Questionnaires show that students trust their peers and believe that the peer-review activity helps to improve the quality of their texts. Value: These results highlight the importance of making students aware of how to improve their texts to get more out of peer review.