This longitudinal study assessed the emergence of gender differences in over 300 children's academic competency beliefs from kindergarten or first grade through fifth grade. Children, their parents and their teachers rated the children's competencies in math and literacy and their math and literacy skills were also assessed directly. Beginning in third grade, girls rated their math competencies lower than did boys, even though there was no gender difference in math achievement or in teachers' ratings of children's math ability. Parents also rated boys' math competencies higher than girls in both third and fifth grades. Although girls outperformed boys on the literacy achievement measure in third and fifth grade, and teachers' ratings of children's literacy ability reflected this gender difference in performance, gender differences were not found in either parents' or children's ratings of literacy ability. Results of regression analyses indicated that actual achievement and teachers' ratings predicted children's judgments of their literacy skills. Parent ratings of children's competence were a particularly strong predictor of children's judgments of their math skills.