When to conduct a functional behavioral assessment (FBA) is a question answered by both best practice and the law. The special education field continues to improve the effectiveness and efficiency of the functional behavioral assessment, an evidence-based technology that is the basis of a behavior intervention plan (BIP) and a cornerstone of the process known as positive behavioral interventions and supports. For children who engage in challenging behavior, the combined FBA, BIP and PBIS processes are aimed at replacing targeted problem behavior with acceptable alternative behavior so the student can make social and academic progress. This commentary answers the question of when to use an FBA by describing what the authors have learned about FBA and suggesting future directions.