Eye and head movements evoked in response to obvious visual attention shifts. However, there has been little progress on the causes of absent-mindedness so far. The paper proposes an attention awareness system that captures the conditions regarding the interaction of eye gaze and head pose under various attentional switching in computer classroom. Via the algorithm of complexion area detection, eye location and eye tracking, the system detects the shifts of the subject's attention, records it and sends a notification to the class teacher. In five variant experiments of attentional shift, the authors find the cues of subjects when turning to other directions, moving forwards or backwards, and closing eyes. It applies even if the students wear glasses or have hair fringe. The findings of absent-mindedness are very important for psychologists or educators conducting post-hoc analysis. These experimental results show eye tracking are useful for detecting shift of attention.