This study investigated the belief that student attention declines after the first 10 to 15 min of class by analyzing vigilance decrement in a guided inquiry physical science course. We used Tobii Glasses, a portable eye tracker, to record student gaze during class sessions. Undergraduate students (n = 17) representative of course demographics (14 female, 3 male) wore the eye tracker during 70-min classes (n = 84) or 50-min classes (n = 26). From the gaze point and fixation data, we coded participant attention as either on-task or off-task for every second of data. This analysis resulted in a percentage of vigilance time on task for each minute as well as the amount of time that participants spent looking in various locations during the class sessions. Participants exhibited on-task vigilance percentages starting with 67% at the start of class and rising to an average of above 90% on-task vigilance at the 7 to 9-min mark with minor fluctuation. Contrary to the belief that attention declines rapidly during a class, the participants on-task spans were larger and more numerous than their off-task spans. These results seem to support the conclusion that well-structured classes punctuated by student-student and instructor-student interactions can be an effective method of maintaining student attention vigilance for entire class sessions, not just the first 10 min.