After students acquire a skill, mastery often requires them to choose to engage in assigned academic activities (e.g., independent seatwork, and homework). Although students may be more likely to choose to work on partially completed assignments than on new assignments, the partial assignment completion (PAC) effect may not be very powerful. The current studies were designed to replicate previous research and determine whether the amount of sunk effort was related to PAC effect strength. Together, these studies (1) provide the only current replication of PAC effect; (2) support previous research, which suggests that the PAC effect is not very powerful; and (3) extend the theoretical research on PAC effects by showing that sunk effort did not influence PAC effect strength. Discussion focuses on implications for educators and directions for future theoretical research designed to identify the causal mechanism responsible for the PAC effect.