Online plagiarism tutorials are increasingly popular in higher education, as faculty and staff try to curb the plagiarism epidemic. Yet no research has validated the efficacy of such tools in minimizing plagiarism in the sciences. Our study compared three plagiarism-avoidance training regimens (i.e., no training, online tutorial, or homework assignment) and their impacts on students' ability to accurately discriminate plagiarism from text that is properly quoted, paraphrased, and attributed. Using pre- and postsurveys of 173 undergraduate students in three general ecology courses, we found that students given the homework assignment had far greater success in identifying plagiarism or the lack thereof compared with students given no training. In general, students trained with the homework assignment more successfully identified plagiarism than did students trained with the online tutorial. We also found that the summative assessment associated with the plagiarism-avoidance training formats (i.e., homework grade and online tutorial assessment score) did not correlate with student improvement on surveys through time.