This research examined whether the tendency for girls to outperform boys in the classroom is due to differences in how girls and boys approach schoolwork. In 5th grade and then again in 7th grade, children (N=518) reported on how they approach schoolwork (i.e., achievement goals and classroom behavior), their learning strategies, and their self-efficacy in math; math grades and achievement test scores were also collected. Girls were more likely than boys to hold mastery over performance goals and to refrain from disruptive classroom behavior, which predicted girls' greater effortful learning over time. The sex difference in learning strategies accounted for girls' edge over boys in terms of grades. Girls did not do better on achievement tests, possibly because self-efficacy, for which there was also no sex difference, was the central predictor of performance on achievement tests.