Since its development in the early 2000's, the Learning Assistant Model for supporting reform in undergraduate STEM education has been implemented in colleges across the nation and the globe. This model consists of adding near-peer learning assistants (LAs) into undergraduate classrooms as part of the instructional staff. Learning assistants take a pedagogy course, actively participate in instructional staff meetings, and interact with students during class, office hour, or lab sessions to draw out reasoning and deepen sense-making and student-to-student interaction. Studies across multiple STEM disciplines have shown repeatedly that student learning outcomes are higher in STEM courses supported by LAs than in courses without LAs. However, important questions remain about the mechanisms through which learning assistants foster improved learning outcomes and about how learning assistants learn to enact these mechanisms. In engineering education, one set of questions asks about the nature of interactions between LAs and their students and among LAs themselves. To begin to understand how engineering LAs interact with students and each other, I conducted three qualitative case studies of engineering learning assistants in various contexts. The first study zooms in on a sophomore-level mechanics course and looks at how two learning assistants and a professor interact with students while they work on an open-ended modeling problem. The second study focuses on the mechanical engineering learning assistants as a group and characterizes the community that they have formed. The third study explores how a learning assistant in a junior-level instruments and experiments laboratory course navigates her role in this skills-focused learning environment. These findings illuminate the various ways in which LAs interact in engineering contexts. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]