Despite the abundant evidence for the general decline in interest during the time spent at school, less is known about the implications of school transition for these declining trajectories of interest. While both Basic Psychological Needs Theory and Stage-environment Fit Theory suggest that students’ interest declines after school transition, they do not clearly predict the nature of the decline. However, there are two possible ways in which interest decreases as a function of school transition: a discontinuous drop during the transition (the immediate impact hypothesis) and a steeper decline during secondary school (the long-term impact hypothesis). Using four years of annual longitudinal data from Japanese students from the fifth grade to the ninth grade, the present study will investigate the developmental trajectory of students’ interest during the period that includes school transition. The impact of SES and gender on the developmental trajectories of interest during the period that includes school transition will also be examined.