Empirical findings have repeatedly demonstrated that students' motivation decreases over the course of secondary education. This decline in learning motivation is one of the top challenges nowadays and is relevant for policy, as well as research and practice. Taking this educational challenge into account, the chapter targets the following questions: (1) Is a multicomponent, two-year intervention (combined student/teacher versus student-only intervention group) effective regarding the self-determined motivation and academic self-concept in mathematics of at-risk students? (2) How effective is the intervention for students with and without a migration background? And more generally: (3) Does the motivation (including students' academic self-concept as a motivational self-belief) differ between students with and without a migration background at three different time points (beginning of Grade 7, end of Grades 7 and 8)? The results indicate that the intrinsic motivation of the combined intervention group could be fostered in the first intervention year. No significant treatment effect could be detected for the student-only group. In line with prior research, students with a migration background demonstrated higher levels of autonomous and controlled forms of motivation. However, students with and without a migration background did not develop differently across the two years. Implications for intervention research addressing adolescents' self-determined motivation are discussed. [For the complete volume, "Motivation in Education at a Time of Global Change: Theory, Research, and Implications for Practice. Advances in Motivation and Achievement. Volume 20," see ED661944.]