There has been much research concerning functional assessment over the past 20 years, but several important research considerations have yet to be explained. One is the comparison of different types of functional assessment (e.g., experimental functional analysis and non-experimental functional assessment). The current study aims to compare the different methodologies of functional assessment and their effectiveness in ascribing function to a target behavior and in the treatment selection that follows such an assessment. Quantitative synthesis data were used to answer questions regarding behavioral function, assessment type, and treatment effectiveness. Results indicate that assessment type can impact treatment effectiveness and that there is a relationship between behavior type and ascribed function.