This project, a multiple case study, was conducted to learn more about the conditions under which teacher collaboration might be expected to occur; to improve understanding of variation in the form of collaboration among teachers; and to understand more about the consequences of such activity on teachers and students. Data were collected from 95 interviews in 4 elementary schools. One of these schools was subsequently dropped for failing to meet selection criteria. The findings, based on 72 interviews in the remaining 3 schools, suggest that consequences of teachers' collaborative efforts are substantial. Extrinsic rewards such as instrumental use of knowledge and support for teacher decision making tended to be limited to information exchange, joint planning, and participatory interactions. Intrinsic rewards were also derived from such encounters but were more strongly associated with deeper levels of joint work. Salient intrinsic rewards included more efficient communication and development of shared meaning, improved teacher efficacy, a sense of belonging, and enhanced understanding of students. Organizational conditions, including principal coordination and support, and collaborative norms in the schools, supported the sorts of teacher-teacher interaction observed. Appendices include a teacher-teacher interaction profile, interview guides, case description assessment form, cover letters, and notes for data analysis. (LL)