Peer Led Team Learning (PLTL) is an effective and interactive approach to teaching mathematics and science. This approach involves the course instructor and peer leaders working with teams of students in weekly workshops. In this article, the authors state that peer leaders play a key role in the success of the peer learning teaching method. They discuss the effect team learning has had on peer leaders in chemistry and biology classes over the course of 4 years at the University of Portland. Moreover, they use the formative assessment tools of journal writing, reflection essays, and anonymous surveys to make a formative assessment of the approach on the peer leaders. (Contains 2 tables.)