At large universities, it is common for a teaching assistant (TA) to have a prominent role in an undergraduate laboratory course. Therefore, they have a direct impact on the experience of the students in the laboratory. The training, background, and motivation of these TAs vary. The motivation of the students in the course also varies. This study sought to answer this question: how do TAs influence the students' learning experience in a required laboratory course? In the fall semester of 2014, at a large public university in the Midwest, TAs were observed in the laboratory sections of a required, juniorlevel course in general engineering. Additional data were obtained from student reflections in each laboratory report and an end of semester survey. Reflections were also collected from students enrolled in the same course in the spring semester of 2015. Finally, at the end of the spring semester, students from both semesters participated in a focus group about the course. The data were analyzed using values coding, which identified values, beliefs, and attitudes expressed by students about the course or the TA. Due to the TAs' prominent role in the laboratory setting, they had a direct impact on the students' experience in the laboratory. However, the impact was different among students who had the same TA. Some of the negative impacts reported were unclear expectations for success, inconsistent grading, and being unavailable or unhelpful. Some positive impacts were also reported, including being helpful and patient. Since data were only collected from the students, the motivations of the TAs were not clear. In this study, there was evidence that the TAs had a negative impact on the learning experience for some students, but not all. To reduce the negative impact in future courses, systems of training, assessment, and accountability for TAs could be improved.