A great deal of research has examined math development in males versus females. Some studies indicate that males do better on standardized tests of mathematics achievement, whereas females get better grades in math class than males. Other studies find no gender differences in math development, or that differences depend on factors such as the type of math problem included on the tests. Further, there is evidence that gender differences in math test performance are not stable over time, with accumulating evidence that these differences are narrowing in more recent cohorts. In addition to evidence concerning sex differences in math grades and test performance, there is evidence that there are sex differences in math attitudes, with females showing higher levels of math anxiety and less confidence in their math ability than males, controlling for their math performance. Additionally, there is evidence that stereotypes exist such that teachers and parents believe that males are better at math than females, even when males and females have comparable levels of math skill. Moreover, when this math stereotype is activated before taking a math test, stereotype threat ensues and female performance is negatively affected. A wide range of factors, including biological differences, sociocultural factors, including stereotypes, and differences in math attitudes and interests, are likely to act in concert to account for male-female differences in mathematics achievement and decisions to enter math-intensive careers.