This mixed methods study examined the influence informal learning experiences had on secondary STEM preservice teachers' preparation as they worked with students who struggle in mathematics. The quantitative data sources included a Teacher Self-Reflection Survey, Mathematics Clinic Tutor Survey, and a Student Survey, while the qualitative data sources were written reflections and semistructured interviews. The informal learning environment simulated a situation in which the tutors were able to practice instructional methodologies in real, contextual situations. The results indicated a positive change in preservice teachers' confidence with mathematical content, while also revealing the need for preservice teachers to have more work with high school mathematics content. Moreover, the experience positively affected the preservice teachers' ability to learn about and implement research-based instructional strategies to work with struggling mathematics learners. All of the preservice teachers cited this experience as the most beneficial learning experience in their teacher preparation program.