Both of the national reform efforts (AAAS, 1993; NRC, 1996) encouraged teachers to engage in professional development that included authentic scientific research experiences. The Department of Energy developed a program to match teachers with mentor scientists at national laboratories for three consecutive summers. Teachers produced and presented a poster summarizing their research at the conclusion of each summer. The purpose of this qualitative multiple case study was to better understand how scientific research experiences impacted teachers. Six dimensions were examined: trajectory of participation, content knowledge development, mentor relationships, beliefs about the nature of science, teacher confidence, and classroom practice. These six dimensions were integrated into three research questions which guided the research: the teachers’ ability to increase their level of participation from the first to the last summer of research, the teachers’ changes in their understanding of the nature of science (NOS), and any changes in the teachers’ classroom teaching because of their involvement in the program. In-depth interviews were triangulated with teachers’ posters to provide insights into teachers’ legitimate peripheral participation in the research laboratory. The VNOS-C (Lederman et al., 2002) was administered pre/post to the teachers. Evidence of more informed, developing, and more naive understandings of each of the tenets of NOS was collected and compared to identify changes in teachers’ beliefs. Interviews and follow-up correspondence informed the study of changes in classroom teaching. The teachers became very familiar with their mentors’ research, increased their subject content knowledge, and contributed to their mentor’s work. Mentors utilized teachers’ expertise as communicators when presenting research and hosting other student groups. The teachers’ understanding of the NOS did not change as a result of their immersion in the culture of the laboratory. The lens through which the teachers viewed science influenced how they perceived and interpreted their research experiences. Teachers who held positivist views reinforced them, while the lone teacher who held post-positivist views reinforced their positions. The teachers developed confidence in their ability to facilitate classroom inquiry, increased the number of inquiry-based in their curriculum, introduced advanced placement and scientific research courses, and rejuvenated their enthusiasm for teaching.