RecruitingBehavioural interventionManualized Assessment and Treatment Model of Challenging BehaviorDespite decades of mounting single-case-design evidence for the efficacy of applied behavior analysis (ABA) and other approaches for the assessment and treatment of challenging behavior, an evidence-based comprehensive approach remains to exist. The current study will collect test the efficacy of a standardized manual for assessing and treating challenging behavior for individuals with severe and mild challenging behavior.