Motivational beliefs of children in grades 5 through 8 (ages 10 years, 9 months to 13 years, 7 months) were assessed in a cross-sectional and a longitudinal study. Children attended a nonsectarian, private school in which the method of evaluating academic performance changed over grades from an individualized, mastery-oriented approach to a normative, comparative one. The school served families of middle to upper-middle SES levels. Only 9% of the children were of minority backgrounds. Children were asked to respond to questionnaires assessing beliefs concerning goal orientations, the value of school, attributions of academic success and failure, and perceived academic competence. Sixty-five of the original 122 children again completed the questionnaire 2 years later. In each study, children's motivational beliefs changed over grade level, so that mastery orientation, perceptions of the value of school, and the use of effort attributions for academic success all decreased over grades 5 through 8, while work avoidance increased. (Author/DR)