Abstract: This study evaluated the influence of group size on student performance and self-reported intrinsic motivation in technology-facilitated formative peer assessment. A sample with 56 students was separated into groups containing 3 or 6 members each to conduct a peer assessment activity via a social messaging app. The smaller groups of students outperformed the larger groups on their essay. Data analysis also indicated the 3-student groups showed higher intrinsic motivation than those in the 6-student groups. Implications and limitations are discussed.