The current study evaluates the concurrent relationship between parent ratings of executive functioning and maladaptive behavior among children and adolescents with Down syndrome and then repeats this evaluation using teacher reports. Parents and teachers of 63 school-age children with Down syndrome rated the child's executive functioning (Behavior Rating Inventory of Executive Function) and behaviors (Achenbach Child Behavior Checklist). For parent and teacher ratings, elevated behavior dysregulation predicted higher levels of rule-breaking, aggressive, and externalizing behavior. For teacher ratings, elevated behavior dysregulation also predicted higher levels of inattention problems. Among both parent and teacher ratings, greater metacognitive difficulties predicted challenges with attention. Understanding the relationship between these constructs has important implications for targets of intervention and developing preventative strategies.