The objective of this and other systematic reviews by the American Academy for Cerebral Palsy and Developmental Medicine (AACPDM) is to provide the biomedical research and clinical practice communities with current knowledge about evidence supporting various interventions used in the management of developmental disabilities. “Systematic, evidence-based reviews are innovative in their comprehensive review of the literature, use of standard methods of presenting data, and special emphasis on the validity of research methods.” (p.470) AACPDM reviews summarize what is known and not yet known, to identify the gaps in our information about treatment outcomes and to gauge the strength of the internal validity of that evidence.