The growing number of peer assessment studies in the last decades created diverse design options for researchers and teachers to implement peer assessment. However, it is still unknown if there are more commonly used peer assessment formats and design elements that could be considered when designing peer assessment activities in educational contexts. This systematic review aims to determine the diversity of peer assessment designs and practices in research studies. A literature search was performed in the electronic databases PsycINFO, PsycARTICLES, Web of Science Core Collection, Medline, ERIC, Academic Search Premier, and EconLit. Using data from 449 research studies (derived from 424 peer-reviewed articles), design differences were investigated for subject domains, assessment purposes, objects, outcomes, and moderators/mediators. Arts and humanities was the most frequent subject domain in the reviewed studies, and two-third of the studies had a formative purpose of assessment. The most used object of assessment was written assessment, and beliefs and perceptions were the most investigated outcomes. Gender topped the list of the investigated moderators/mediators of peer assessment. Latent class analysis of 27 peer assessment design elements revealed a five-class solution reflecting latent patterns that best describe the variability in peer assessment designs (i.e. prototypical peer assessment designs). Only ten design elements significantly contributed to these patterns with an associated effect size R[superscript 2] ranging from 0.204 to 0.880, indicating that peer assessment designs in research studies are not as diverse as they theoretically can be.