A usability study was undertaken at Penn State University to explore how students search the library's online catalog after they have received library instruction. In 2004, eight first-year students received library instruction and were subsequently recruited for the study. Participants were recorded using the online catalog, and a think-aloud protocol was employed to capture students' thoughts. Results were compared with nine first-year students observed in 2002, using the same methodology. Analysis of both groups revealed subtle differences in how they utilized the online catalog. Although these differences cannot be definitively attributed to library instruction, the evidence suggests that instruction can have a positive effect on user search behaviors. The article recommends strategies for increasing the impact of library instruction. (Contains 35 notes.)