Contribution: This study identifies the types of interaction that contribute to student learning with student-led tutorials (SLTs). The quality of these interactions include peer discussion, student tutor presentation, joint reasoning, and constructive feedback. Background: The introduction of SLTs in an advanced electromagnetics bachelor course has improved the passing rates from 40% to 60%. SLTs, as one type of peer learning and tutoring, correlate with active learning and student achievement. However, there is not much knowledge about the different kinds of student interactions and its respective impact on learning. Research Question: How students' interactions contribute to students understanding of content and problem-solving skills in electromagnetism and what influences the quality of such interactions? Design/Method: The study inductively analyzed different sources of data that included classroom observations, student surveys, focus groups, and interviews to identify SLTs interactions. Findings: SLTs contributed to student understanding of concepts, practicing general engineering problem-solving skills, and keeping pace with the course activities. The quality of students' presentations, the type of questions that tutors posed, the tension between revising all problems in broader terms and discussing concepts in-depth, the difficulty of content knowledge and tutors' understanding of the problems; influenced the quality of SLT interactions. This research finds that, while in general SLT promotes learning, teaching students how to actively participate and training teaching assistants how to organize classroom interactions, can further contribute to in-depth conceptual discussions of the subject matter.