This study examined the effect of the Building Blocks mathematical education program on 4-year-old Turkish preschool children's recognition level of geometrical shapes. A pretest-posttest control group experimental design was employed. The sample group was composed of randomly selected 39 preschool children (of whom 21 were in the experimental group, and 18 in the control group). A geometric shapes recognition test was used for data collection. Results indicated meaningful differences in the mean scores of the triangle and rectangle shapes in favor of the experimental group. When the children's responses to the geometric shapes recognition test were examined in detail, it was observed that in the post-test the children in the experimental group, as compared to the ones in the control group, were more inclined to define geometrical shapes with their qualitative features rather than visual features.