This report presents a literature review and conceptual model summarizing the influence of peer effects on learning outcomes. The report describes the approach to the review and provides a theoretical account of the environments, mechanisms, and processes that mediate learning among peers. It then summarizes the literature on compositional effects at each level of school organization--groups, class, and school--and suggests how these effects might implicate peers by making connections to the theoretical account of peer-mediated learning. Next, the report makes linkages across different levels of inquiry in order to develop a conceptual model of peer influences on learning. A multi-layer model is proposed, with effects propagating from school-level influences to class-level influences to group-level influences to ambient and configured environments for learning among peers. It is proposed that the bulk of the effects are indirect; hence, peer effects "look" smaller the further one moves away from the instructional coalface because they are mediate by intervening layers. It is noted that there may also be reciprocal effects whereby peers influence teachers and school organization and management, although the magnitude of these effects is undetermined. In concert with the three layers of influence, it is argued that family resources have greater effects at uppers layers and smaller effects at the lower layers; conversely, curriculum and teaching resources have greater effects at lower layers and smaller effects at upper layers. Home and school supports for learning carry the lion's share of the weight in predicting student learning outcomes, whereas peer effects, as currently constituted, carry much less weight. Finally, the report describes four instructional approaches that utilize peer resources to maximize learning. These models demonstrate additional ways of capitalizing on peer effects beyond altering student composition. (Contains 637 references.) (Author/HTH)