Teaching assistants (TAs) are crucial for student learning, especially in large science, technology, engineering, and mathematics (STEM) programs with student-centered learning environments. To understand TAs' perspectives of their ability to facilitate learning in these environments, this research team conducted a mixed-methods study. This study was set in the First-Year Engineering Program at Purdue University. The TAs for this program are responsible for scaffolding student teams' learning through feedback on open-ended problems, along with some other traditional TA duties (e.g., grading student work, answering student emails). The study began with a qualitative component in which eight TAs were interviewed about their abilities to execute their various responsibilities. Based on these interview findings and literature, a survey was developed to further investigate key elements that the TAs discussed (e.g., motivation and feedback). Forty-three TAs completed the survey. Based on the analysis of TAs' responses, two regression models were made that describe the factors that effect TAs' self-reported likeliness to give effective feedback and ineffective feedback. TAs with intrinsic motivation were more likely to give more effective feedback, while TAs with extrinsic motivation were more likely to give more ineffective feedback. Also female TAs reported giving less feedback in general than male TAs.