ABSTRACT
Although I agree with many aspects of Zigler's “developmental” theory of retardation, several points appear to merit further discussion and clarification. A key portion of his developmental theory (Zigler, 1967) is given in the following:
the familial retardate's cognitive development differs from that of the normal individual only in respect to its rate and the upper limit achieved. Such a view generates the expectation that, when rate of development is controlled, as is grossly the case when groups of retardates and normals are matched with respect to mental age, there should be no difference in formal cognitive processes related to I.Q [p. 294].
