Optimizing Peer Grading: A Systematic Literature Review of Reviewer Assignment Strategies and Quantity of Reviewers

Peer assessment has established itself as a critical pedagogical tool in academic settings, offering students timely, high-quality feedback to enhance learning outcomes. However, the efficacy of this approach depends on two factors: (1) the strategic allocation of reviewers and (2) the number of reviews per artifact. This paper presents a systematic literature review of 87 studies (2010--2024) to investigate how reviewer-assignment strategies and the number of reviews per submission impact the accuracy, fairness, and educational value of peer assessment. We identified four common reviewer-assignment strategies: random assignment, competency-based assignment, social-network-based assignment, and bidding. Drawing from both quantitative data and qualitative insights, we explored the trade-offs involved in each approach. Random assignment, while widely used, often results in inconsistent grading and fairness concerns. Competency-based strategies can address these issues. Meanwhile, social and bidding-based methods have the potential to improve fairness and timeliness -- existing empirical evidence is limited. In terms of review count, assigning three reviews per submission emerges as the most common practice. A range of three to five reviews per student or per submission is frequently cited as a recommended spot that balances grading accuracy, student workload, learning outcomes, and engagement.