This paper examines STEM-based informal learning environments for underrepresented students and reports on the aspects of these programs that are beneficial to students. This qualitative study provides a nuanced look into informal learning environments and determines what is unique about these experiences and makes them beneficial for students. We provide results of a qualitative research study conducted with the Mathematics, Engineering, Science Achievement (MESA) program, an informal learning environment that has proven to be effective in recruiting, retaining and encouraging underrepresented students to pursue STEM careers. Using a grounded theory approach, focus group interviews were conducted with five student groups throughout the state of California in an effort to "unpack the activity" variables of the informal learning environment. Results of this study should inform formal learning environments and other informal learning environments as to the components that make these learning environments effective and appealing to underrepresented students populations.