The use of functional behavioral assessment (FBA) is an effective tool to address a wide range of severe behavior problems of students at risk for or with emotional disabilities (ED). However, the transformation of a procedure proven effective under highly-controlled clinical conditions to a practical and effective strategy for use in applied settings has posed a number of challenges. We critically examine several of the most prominent of those challenges and related research. We concede that there is more to learn about FBA in applied settings, including how best to establish a goodness-of-fit between "necessity and sufficiency," as described by Scott and Kamps (2007). Lastly, we assert that all school personnel should, at the very least, "think functionally" about pupil behavior.