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EE Maccoby and CN Jacklin (1974) concluded that the following cognitive gender differences were well-established: verbal ability, quantitative ability, and visual–spatial ability. The present study applied meta-analysis techniques to studies cited by Maccoby and Jacklin, assessing the magnitude of gender differences using both ω–2 and d statistics. Results indicate that gender differences in all of these abilities were small: For verbal ability, the median ω–2 was. 01 and the median d was. 24; for quantitative ability, the median values of ω–2 and d were. 01 and. 43; for visual–spatial ability, they were. 043 and. 45; and for field articulation, ω–2 was. 025 and d was. 51. Discussion focuses on the practical implications of the finding that these" well-established" differences were in fact very small. Concerns about sampling are raised. The problem is also discussed in the context of a larger issue in psychological research …