This article explores the reasons that Peer Assisted Study Sessions (PASS) at the University of the Incarnate Word (UIW), commonly called PASS-UIW, has been successful in science courses at the University. The intent is to provide information for other institutions to launch, evaluate, or improve their own programs. PASS-UIW is a student-led program to assist undergraduate students taking Chemistry and Physics gateway courses. PASS-UIW has shown improved student engagement and created an opportunity for student leaders to gain valuable experience teaching peers. Several key criteria have been identified as impacting the success of the program: 1) extensive training, 2) use of collaborative learning techniques, 3) communication among constituents, and 4) dedication of leaders and faculty. (Contains 7 figures.)