Especially for students in lower achievement levels, there is a significant negative trend in academic self-determined motivation across childhood through adolescence and more so in maths than in any other school subject. To counteract this negative development, a multicomponent intervention study based on the main ideas of self-determination theory, students' emotions in relation to maths, and the concept of self-regulation was developed and implemented in Swiss seventh-grade maths classes with basic demands. The study applied a quasi-experimental design comparing two experimental groups (combined student/teacher group: teachers and students participated in the intervention; student-only group: only students participated in the intervention) and a control group. Intervention effects were evaluated longitudinally (pre-post test) via self-reports of 348 students. Within-group results (t tests) showed no significant changes for students in the control group, a significant decrease in intrinsic and identified motivation for students in the student-only group, and a significant increase in intrinsic motivation and self-concept for students in the combined student/teacher group. Multivariate analyses of covariance controlling for pre-test variables as well as gender and migration background showed significant group effects. As the most positive effects were found for students in the student/teacher group, the results highlight the importance of co-constructed teaching and learning.