Despite school-based services, adolescents with maladaptive behavior experience negative outcomes, highlighting the need for insight into factors that contribute to and escalate behavior problems during middle school--a high-risk period. We examined how perceived school stress, stress regulation (engagement/disengagement coping, involuntary responses), and executive function of 79 middle schoolers with and without significant behavior problems were related to internalizing and externalizing behaviors. Results showed students with significant behavior problems (a) had lower executive function abilities and higher peer stress, (b) used less engagement coping, and (c) reported more maladaptive behaviors than typical peers. For all students, school-based stress positively predicted behavior problems and use of stress regulation techniques, with group moderating effects. Involuntary responses to stress positively predicted maladaptive behaviors, whereas engagement/disengagement coping predicted internalizing behaviors only. As a mediator, engagement coping decreased the relationship between perceived stress and behavior problems. Based on these findings, we highlight important prevention and intervention areas.