This study examines how well second-year nonmajor organic chemistry students are learning to draw, interpret, and understand resonance-related structures. Students were tested seven times throughout an academic year using a set of four tasks that reflected their understanding of what these structures represent and how they relate to each other. Statistical analysis was used to validate the tests, to investigate whether the tasks were mastered, and to examine possible correlations between the tasks and between each task and students' grades in the course. These data were also analyzed to determine which tasks were deemed most difficult and to identify the most common errors associated with each task. This study seeks to raise consciousness of areas that prove to be most difficult for students and that could be limiting their mastery of the resonance concept. (Contains 5 tables and 5 figures.)