Ed Zigler's developmental approach to intellectual disabilities: Past, present, and future contributions.

Comprising two parts, Ed Zigler's developmental approach has greatly influenced how one conceptualizes children with intellectual disabilities (ID). In part one, Zigler championed a "two-group approach" concerning the cause of children's ID. He distinguished persons with a clear, organic cause of their ID from those displaying no clear cause. Members of this "organic" group often displayed IQs below 50 and co-occurring physical-medical conditions. The second, "cultural-familial" group, mostly showed IQs of 50-70, did not possess co-occurring physical or health problems, and often came from families of lower IQs and lower socioeconomic status. While the presence of these two groups has been supported, recent advances have also further differentiated the organic group, mostly in relation to behavioral phenotypes of persons with several genetic etiologies. In part two, Zigler championed the child with ID as a "whole person." Originally focused on the child's reactions to social deprivation and failure, recent studies directly examine parent-child, within-family, and wider system interactions throughout the life span. For decades a force within the ID field, Zigler's developmental approach to children with ID continues to influence researchers, interventionists, and policymakers.