This study explored how teachers’ functionality as scientists developed and aspects of their experiences that were important to their development as scientists. These results suggest that a teachers’ background before participating in a Research Experiences for Teachers program does not determine whether a teacher will reach high scientific functionality or not. Furthermore, teachers within the high science functionality group adjusted to open-ended environment, transitioned from a guided experience to freedom, felt useful in the laboratory, and were self-motivated. In contrast, the low science functionality group did not have a true research project, primarily focused on teaching aspect, and did not display a transition of responsibilities.