Thoughts drift in everyday life and in the classroom. The goal of this study was to investigate how often students reported off-task thinking while watching online lectures. These findings were related to working memory capacity, topic interest, and achievement goal orientations. Structural equation modeling was used to evaluate how all of these factors were related and predicted performance in the course. In the presented findings, 126 participants completed three complex span tasks, answered a 2x2 goal orientation questionnaire, responded to eight mind-wandering probes while watching two online lectures, and rated interest in the lecture topics. In the reported models, higher levels of mind wandering predicted lower levels of academic performance. Lower levels of working memory capacity predicted higher levels of mind wandering and lower levels of academic performance. Higher levels of topic interest predicted lower levels of mind wandering. Higher levels of mastery approach orientations (those who learn to master content) predicted higher levels of task-related interference. A novel mind wandering probe, "thinking about or using another technology," accounted for 29% of off-task thinking. Implications of these findings and considerations for future research are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]