Rehearsing in front of a live audience is a common practice when preparing for important presentations. However, not everyone has the opportunity to do this, due to time constraints, availability of listeners who can provide constructive feedback, or public speaking anxiety. RoboCOP is a fully-automated anthropomorphic robot that acts as a coach to provide feedback during presentation rehearsals at both the individual slide and overall presentation level. The robot offers conversational coaching on three key aspects of presentations: speech quality, content coverage and eye contact. The design of the feedback strategies was informed by findings from an exploratory study with academic professionals who were experienced in mentoring students on their presentations. Results of our within-subjects evaluation study show that our system creates a natural, interactive and motivating rehearsal environment that leads to improved presentation quality.