Schools face an increasing need to develop effective strategies for fostering social inclusion in educational settings, yet it remains unclear which factors might hinder or promote adolescents’ engagement in socially inclusive behaviors in diverse school settings. This study aimed to examine the association adolescents’ attitudes toward diversity and their willingness to engage in inclusive behaviors and whether the classroom social climate moderates this association. The sample included 1065 adolescents residing in Sweden (Mage=13.12, SD=.42; 55% males). Multilevel modeling at two analytic levels was conducted. At the individual level, we found that female adolescents and those with high levels of openness to diversity were more willing to engage in socially inclusive behaviors. At the classroom level, positive inter-ethnic contact norms were associated with increased inclusive behaviors among adolescents, whereas negative inter-ethnic contact norms showed the opposite effect. Furthermore, perceived negative inter-ethnic contact norms in class significantly moderated the association between adolescents’ openness to diversity and their willingness to engage in socially inclusive behaviors. Specifically, adolescents with high levels of openness to diversity were less likely to engage in socially inclusive behaviors when they perceived their class context as not valuing and appreciating diversity. These findings underscore the potential influence of both individual and contextual factors in the formation of inclusive behaviors. Importantly, adolescents with greater openness to diversity seem to be constrained to show their potential for engaging in socially inclusive behaviors when diverse views and values are not appreciated and respected, and prejudiced behaviors are tolerated in their class context.