Group configurations play a pivotal role in shaping social skills and learning outcomes by fostering student interaction and collaboration. Yet, the factors influencing group formation, social cohesion, and group stability remain understudied. Here, we examine these factors in a cohort of 90 students from 9th and 10th grades at a private school in Chile. Students were either randomly assigned to groups (control) or allowed to choose their own groups (experimental) for a semester-long project. Our results show that self-selected groups had stronger friendship ties by the end of the semester. In contrast, randomly assigned groups exhibited higher levels of cooperation and more frequent membership changes, indicating weaker social cohesion. Additionally, 10th-grade students were more likely to stay in their original groups, possibly suggesting increased social maturity. These findings underscore the ongoing challenge in education of balancing student choice in group formation with the need for diverse group compositions that enhance learning. The study provides actionable insights for educators.
