The changes in adolescents' math motivational beliefs (i.e., expectancies for success, interest, and utility value) across Grades 9-11 and the associations between these changes and adolescents' experiences with socializers (i.e., perceived teacher unfairness and parent-adolescent discussions) were examined within each of the four largest racial/ethnic groups in the United States using the High School Longitudinal Study, a nationally representative data set (n = 19,010; 50% female; 9% Asian; 11% Black; 18% Latine; 62% White; Mage = 14.53 in Grade 9). Cross-tabulation analyses suggested that similar developmental trends emerged within each racial/ethnic group (which were tested separately). Many adolescents maintained their high or low expectancies, interest, and utility values across Grades 9-11. Some patterns varied by belief; for example, several adolescents switched from high to low interest by Grade 11, whereas several adolescents switched from low to high utility value. Parent-adolescent discussions predicted positive changes among Asian and Latine adolescents, whereas perceived teacher unfairness predicted negative changes among Black adolescents. The findings from the present study highlight the diverse developmental trends in adolescents' motivational beliefs and the potential role of socializers as sources of strength or challenge in their motivational belief development. (PsycInfo Database Record (c) 2024 APA, all rights reserved).