Behavior analysts have had a significant impact on the analysis and interve
ntion of challenging behaviors in persons with developmental disabilities.
These successes are celebrated in the first parr of this article. In the re
mainder of the article,ye present a selective discussion of three issues th
at we hope will help to further stimulate work with challenging behaviors:
(a) the development of challenging behaviors, (b) the role of rule-governan
ce in challenging behavior, and (c) the behavior of persons (mediators) who
directly apply functional assessment and intervention technologies. Each o
f these issues is discussed and implications are drawn for future reseach a
nd practice in the field. In drawing some conclusions, we focus on the inte
rnal and external validity of functional assessment and interventions.