This conceptual article describes a model of a school-based, student-led initiative that uses peer tutoring to address underachievement in mathematics. The model is three pronged: a) it suggests a site-based approach to building on existing student excellence in mathematics to drive improved student mathematics achievement; b) it seeks to address the lack of teacher knowledge about urban students and their mathematics understanding; and c) it aims to deepen existing mathematics knowledge, confidence and interest among high school students. In the article, I share analyses of the interactions among tutors, tutees, advisors, and teacher; the mathematical discourse within those interactions; and the hierarchical and collaborative relationships that emerged over time.