Projects and Practices in Physics (P-Cubed) is a flipped, problem-based learning course for introductory, calculus-based mechanics. P-Cubed was designed using the communities of practice framework, with a principle learning goal to develop scientific practices. To promote students' development of practices, students spend their in-class time working in groups of 4 to 5 members to solve complex physics problems. Scientific practice development is then facilitated through formative feedback and assessments aligned with the growth in these practice. Each student receives weekly, individualized feedback from their instructor (either a faculty member, teaching assistant or learning assistant) as a practice-based assessment. The feedback focuses on helping students improve their individual understanding and group collaboration through the development of key group-based practices such as decision making and planning. This paper reports on a series of semi-structured interviews that were conducted with students at various points in the semester to understand the impact feedback had on them.