Understanding and promoting effective teaching are central concerns of the engineering education community. This paper reports on research to investigate the processes by which construction of teaching portfolios in a socially supportive context can promote the advancement of teaching knowledge and ability. By characterizing how a specific intervention can advance teaching knowledge and effectiveness, findings and ideas are generated that can help others engaged in the same goal. This study looked at the CAEE Engineering Teaching Portfolio Program (ETPP) as a learning event--how the individual and social processes associated with building a teaching portfolio could lead to advancement of teaching knowledge and ability. Participants in the ETPP prepared a teaching portfolio consisting of a teaching philosophy, two to five annotated artifacts, and a diversity statement. Peer review--defined as reciprocal evaluation of written products--was originally conceived as a core element of the program and makes up about half of each ETPP session. Evidence suggests that the peer review periods may be important from the perspective of both learning and other participant outcomes. This and other indicators identified the peer review activities as one of the most important elements of the ETPP. Developing a greater understanding of what is going on during these periods provides insights to programs that create approaches to improve teaching.