Undergraduate students benefit from academic-centered peer interactions, especially in large lecture courses. However, little is known about how students come together and form relationships around a course. I conduct a mixed-methods study of students' peer networks to explore how students choose peers for academic-focused interactions. The network of connections among students in a large undergraduate physics class decreases over time, leaving students looking for study partners later in the course at a disadvantage. While community structure might limit relationship formation late in the semester, students who connected across campus capitalized on network internalities that facilitated opportunities for collaboration.