For students with severe or complex challenging behavior, incorporating hypothesis testing as a component of functional behavior assessment (FBA) is often warranted. Several hypothesis testing strategies (i.e., functional analysis, antecedent analysis, concurrent operant analysis) can confirm whether and how features of a student’s environment impact their behavior to then inform effective intervention. Yet practitioners have limited guidance on how to select and individualize best-fit strategies for a given student and context. We developed a decision tool for behavior specialists and classroom teachers to collaboratively plan and implement individualized hypothesis testing strategies for students whose initial FBA was inconclusive. We piloted this tool with 12 practitioner teams and students, aiming to (a) identify which assessment strategies were indicated based on practitioner responses; (b) evaluate whether indicated assessments produced conclusive results; and (c) explore practitioner perceptions of the individualized assessment process. The most commonly indicated hypothesis testing strategy was functional analysis. Across teams, one or more hypothesis was successfully confirmed on the first or second assessment iteration. The assessment process was perceived positively by practitioners. Yet they reported feeling ill-equipped to complete the process independently, highlighting important next steps for training and technical assistance work.