Higher educational institutions seek to improve the quality and the productivity of the educational process. The current attitude is toward involving students in the learning and evaluation process. Peer review has been proven to be one of the most effective tactics to attain this in software engineering disciplines wherein project-based courses are substantial to afford high quality competencies. A few studies in literature empirically studied the impact of peer review in project-based software engineering courses. In this work, we attempt to provide more insights by implementing peer assessment in one of the project-based courses offered by the department of software engineering at the Hashemite University, Jordan, that is “Object-Oriented Software Development”. In this paper, we investigate the validity of peer assessment by examining how well students in this course evaluate their peers and how the strength of students affects their assessment. The work also embeds a rubric that comprises key criteria to assess software system modelling. The results of the study reveal promising signs of using peer assessment in project-based software engineering courses.