As seen in Table 1, the rank average of the experimental group is 16.46 and control group is 20.14. This means there is no significant difference between pretest scores of experimental and control groups based on the results of Mann-Whitney U-test [U=128.00, p>.05]. Therefore it is proved that the experimental and the control groups are equivalent in terms of Van Hiele geometric understanding levels and neither of the groups overruns the other initially.