Corman and Escalona's scales for Object Permanence and Spatial Relationships were administered to 98 severely and profoundly retarded children on three occasions, with intervals of six months between successive administrations. Correlations between the scores on the three administrations ranged from .76 to .87, and the mean change was less than one point on each of the scales. These findings demonstrate the high stability of the scales when environmental conditions are themselves highly stable.
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