Grounding on expectancy-value theory, this study investigated stability and change in adolescent students' (N = 508) motivational profiles in mathematics (expectancy, values, costs) during the last year of comprehensive education, and how these changes relate to relevant educational outcomes (mathematics performance and aspirations) and students’ well-being (study-related exhaustion and depressive symptoms). Latent profile and latent transition analyses revealed four motivational profiles among students: Positively ambitious (high expectancy and value beliefs, low costs, T1: 34%/ T2: 32%), Struggling ambitious (high expectancy and value beliefs, high costs, T1: 25%/T2: 25%), Indifferent (low expectancy and value beliefs, low costs, T1: 22%/T2: 21%), and Maladaptive (low expectancy and value beliefs, high costs, 19%/22%). Although some fluctuations were detected in profile memberships within the school year, the majority of the students (80%) displayed stable mathematics motivation across ninth grade. Students who remained Positively ambitious also performed well, aspired for an education that required high mathematical skills, and experienced the least problems with their well-being, whereas students in the most negative motivational profile (Maladaptive) showed the opposite patterns. However, students who experienced high math-related costs, despite having positive value beliefs, performance and aspirations (i.e., Struggling ambitious), also experienced one of the highest levels of study-related exhaustion and depressive symptoms. Elevated levels of exhaustion and depressive symptoms were systematically associated with negative motivational transitions in general (i.e., moving from Positively ambitious to Struggling ambitious, or from Indifferent to Maladaptive), highlighting the importance of reducing perceived study-related costs in schools and supporting students' well-being.