Sex differences in children's attributions for success and failure were tested on a group of 165 fifth and sixth graders taking a regularly scheduled math and spelling test in their classroom. Pretest questionnaires measured students' self-perceptions of competence in the subject and their performance expectations on the test. Questionnaires, given after the corrected tests were returned, assessed students' actual performance, subjective ratings of success, attributions for the cause of their success or failure, and performance expectations for future tests. Results indicated that sex differences existed in math but not in spelling: compared to girls, boys perceived themselves to be more competent and did better on the math test. Boys were also less likely to attribute failure on the math test to lack of ability and more likely to attribute success to ability than were girls.