Previous research on stereotype threat in children suggests that making gender identity salient disrupts girls' math performance at as early as 5 to 7 years of age. The present study (n = 124) tested the hypothesis that parents' endorsement of gender stereotypes about math moderates girls' susceptibility to stereotype threat. Results confirmed that stereotype threat impaired girls' performance on math tasks among students from kindergarten through 2nd grade. Moreover, mothers' but not fathers' endorsement of gender stereotypes about math moderated girls' vulnerability to stereotype threat: Performance of girls whose mothers strongly rejected the gender stereotype about math did not decrease under stereotype threat. These findings are important because they point to the role of mothers' beliefs in the development of girls' vulnerability to the negative effects of gender stereotypes about math. (Contains 2 tables, 2 footnotes, and 1 figure.)