The goal of the present studies was to examine whether students' reasoning about the relation between levels of effort and ability is influenced by the perceived source of an individual's effort. Two sources of others' effort were examined: "task-elicited effort," or effort due primarily to the subjective difficulty of the task, and "self-initiated effort," or effort determined by students' own motivation. In 3 studies, undergraduate participants responded to vignettes in which they were asked to make ability evaluations of other students given information about the level of their effort, the source of their effort, and their performance on an academic task. Results from 3 studies indicated that perceived effort source influenced students' ability evaluations, but only in the absence of explicit performance information. When students were led to believe that an individual's effort on an academic task was task-elicited, they were more likely to endorse an inverse relation between levels of effort and ability (i.e., to rate individuals who expended high levels of effort as having less ability than individuals who expended low levels of effort). However, when they perceived this effort to be self-initiated, they were less likely to endorse an inverse relation and in some cases endorsed a positive relation between levels of effort and ability. Implications for education are discussed.