Encouraging students to develop multiple solutions for given problems is an important way to improve mathematical knowledge. However, the influence of this teaching element on students' interest-related motivational orientations is an open question. In this article, we report the results of an experimental study (N = 145) that was carried out to investigate the influence of prompting students to construct multiple solutions for real-world problems with vague conditions on students' interest in mathematics as well as on their experiences of competence and autonomy and the number of solutions developed. A positive effect of the intervention on students' interest was found using inferential and path analyses. The number of solutions developed by students and their experiences of competence and autonomy mediated the effects of prompting multiple solutions on interest. Implications for teaching practices and future research are discussed.