A study was designed to determine the effects of various ball sizes on children's catching ability and to examine the results as a between- and within-group factor. It was believed that the use of the two-test design would help to establish the validity of past and future tests of this nature. The between-subjects design group consisted of 48 first grade children who were required to make a series of catches using one ball size (6 inch, 8.5 inch, or 10 inch diameter). Each of the children on the within-subjects group received a total of 12 trials, catching all three ball sizes in random order. Since the initial analysis showed a significant trials effect as the subjects adapted to the task, data were modified to reduce this effect. Subsequent analyses showed that the only significant interactions in the between-subject design situation was between the size of the ball and the gender of the subject. For the within-subjects design group, only the main effect of the ball size was significant. The 10 inch diameter ball resulted in more successful catching than the 6 inch ball. The two design types appeared to be interchangeable in the paradigm. (FG)