As part of our Physics Education Research Group efforts to transform the physics instruction at Florida International University (FIU), we have focused attention on how to assess the reforms we implement. In this paper, we argue that the physics education community should expand the ways that it measures students' success beyond grades and conceptual inventory scores to include assessments of students' participation in a learning community and changes in their attitudes. We present case studies of three introductory undergraduate physics students' increasing participation in the physics learning community at FIU, which is a large, urban, Hispanic-serving institution. In previous work, we have reported gains in conceptual learning and attitudes about learning science in those students enrolled in the introductory courses at FIU taught with Modeling Instruction, which operates in a collaborative learning environment. This paper expands upon those results in considering the variety of opportunities for participating in the physics learning community and by closely examining three aspect of student participation: students' attitudes about learning physics, their ties within the physics classroom, and their relationships within the physics learning community. This provides a more comprehensive understanding of how students in underrepresented groups may become successful physics learners.