W HEN HANDICAPPED infants andyoung children lack communication skills, function at very basic levels, and are characterized by atypical and/or stereotyped behavior, valid assessment of developmental functioning is difficult, if not impossible. A not-infrequent conclusion is that such children are untestable (Alpern, 1967). A common approach to dealing with these problems has taken the form of extending, simplifying, or otherwise modifying existing normative scales of development. Such efforts have had limited success because of methodological problems of infant assessment in general (Lewis, 1975) and associated concerns of accountability with special populations (Simeonsson,