Experimental designs based on decision-making allow researchers to analyze how participants prioritize individual interests over collective benefits. Previous studies have shown that cooperation tends to decline as group size increases. This study aimed to experimentally examine the influence of group size on adolescents' cooperative behavior.
The sample included 112 students from three educational institutions in Mexico, each with a distinct class size: Group 1 (n = 45), Group 2 (n = 39), and Group 3 (n = 28). From each cohort, three subgroups of four students were randomly selected (total: 9 subgroups, 36 students) to complete a one-time Public Goods Dilemma task over 10 experimental rounds. Additionally, interviews using the Composite Socio-Cognitive Maps (CSCM) instrument were conducted to map the social networks within each group.
ANOVA results revealed statistically significant differences in cooperation levels among the groups (F(2,114) = 24.16, p < .001). These findings provide empirical evidence that overall group size influences cooperative dynamics, even when the task involves the same number of participants over the same duration. The study highlights the importance of reducing classroom sizes in Mexico—where the average group includes 45 students—as a strategy not only to enhance learning outcomes but also to improve social cohesion and cooperative behavior.