The relative influence of interest and self-efficacy beliefs on each other over 1 year was examined in 2 longitudinal samples of students, 1 of elementary school students (Grade 5, N = 126) and 1 of middle school students (Grade 7, N = 221). Interest and competence ratings on the Realistic, Investigative, Artistic, Social, Enterprising, and Conventional scales (J. L. Holland, 1997) were assessed using the Inventory of Children's Activities-Revised (T. J. G. Tracey & C. C. Ward, 1998). Responses were examined using structural equation modeling, and the results demonstrated that there were changes both in the structure and level of interest and competence ratings over time. The circumplex structure was found to become more prominent over time, especially by 8th grade, and overall mean levels of interest and competence ratings decreased over time. Interest and competence ratings were found to predict each other equally over time. Finally, there were significant grade, gender, time, Time x Grade, and Time x Gender effects on the scale score means. Results are discussed with respect to implications for interest development and assessment.