The definition, measurement, prevalence, and relations of mastery-avoidance goals with engagement outcomes are still under debate. Study 1 (n = 256) aimed to investigate these issues among junior high and high school students in two domains. Findings indicated that students distinguished between the three commonly assessed achievement goals and mastery-avoidance goals. Moreover, students distinguished between the two standards conceived to underlie mastery-avoidance goals--task-mastery and intrapersonal competence. However, the task-mastery items failed to show reliability. Study 2 (n = 118) aimed to replicate the results of Study 1 as well as to investigate the associations of mastery-avoidance goals with self-regulation strategies and affect in school. Intrapersonal mastery-avoidance goals were positively related to adaptive strategies and negatively with maladaptive strategies. Moreover, when combined with mastery-approach goals, intrapersonal mastery-avoidance goals enhanced students' reports of adaptive affect in school. The implications of these findings to theory, method, and future directions are discussed. (Contains 7 tables and 5 figures.)