Ss classified a test form as matching or not matching one of a set of memorized forms relative to which the test forms were rotated up to 90 deg. "Match" reaction times increased monotonically with both number of forms memorized and degrees of rotation. Disappearance of the rotation effect after practice was attributed to a change from considering rotational information during comparison to comparing rotation invariant features. The change in strategy is considered an indicant of the development of shape constancy. Time taken to memorize the patterns increased linearly with the size of the memory set, justifying interpretation of the RT effects in terms of comparison time differences rather than differences in memorial specification of the patterns.