The purpose of this article is to document characteristics of kindergarten classrooms that provide resiliency and reduce social and behavioral problems of children during their first year of formal schooling. We analyzed secondary longitudinal survey data of 13,533 kindergartners and 2,411 kindergarten teachers using hierarchical linear modeling to study change in externalizing behaviors and self-control between the fall and spring of kindergarten. Once family background characteristics were controlled, classroom effects such as children's overall behavior were analyzed, as were cross-level interactions between classroom and family effects. The results revealed that good behavior in the classroom and adequacy of classroom supplies were the most consistent predictors of improvement in children's self-control and behavior. Furthermore, cross-level interactions suggested that good behavior in the classroom and supplies can boost resiliency by allowing children to overcome certain deficits at home. Implications for further research and educational policy are discussed.