This study reports on the design, implementation, and evaluation of a service-learning course based on a "cascading mentoring" model linking together the faculty, administration, and undergraduates of an urban university's computer science department with local high school students. We present findings from surveys and post-interviews that illustrate undergraduates' and high school students' experiences in the program and how their perceptions of computing and mentoring changed based upon the outreach. In our discussion, we focus on the institutional and conceptual challenges of implementing the community service course within the university's computer science department, while also highlighting the learning opportunities for streamlining such a model for future iterations.