Functional analysis methodology has become the hallmark of behavioral assessment, yielding a determination of behavioral function in roughly 96% of the cases published (Hanley, Iwata, & McCord, 2003). Some authors have suggested that incorporating the results of a descriptive assessment into the design of a functional analysis may be useful in determining behavioral function when initial functional analyses yield undifferentiated results, yet this strategy has little empirical support to date. This study evaluated the effects of incorporating stimuli observed to occasion problem behavior during a descriptive assessment into the design of a functional analysis that had previously resulted in low and undifferentiated levels of problem behavior. Further, the effects of a function-based treatment derived from the results of the "informed" functional analysis were evaluated across settings (therapy room and preschool classroom) and people (therapist and classroom teachers). The somewhat complex relation between descriptive assessments and functional analyses are discussed.