This article presents results of a case study of a math circle designed for low income, minority students from an inner city middle school. The students were 6th, 7th and 8th grade African American and Hispanic males enrolled in a science, technology, engineering and mathematics focused charter school. The study focused on the impact of participation in the math circle on students and the design features of the experience that were most effective at promoting engagement and positive reactions from students. Participating students reported increases in their interests in mathematics, their confidence in their ability to tackle mathematics problems, and in their enjoyment of mathematics. Competitions and affirmation by a mathematician were key motivating factors for students. Implications for the design of math circles that promote positive mathematical identifies among marginalized populations of students are discussed.