They daydream less and this can affect grades:
The experience of daydreaming is familiar to all, yet daydreaming and its correlates in an educational context have yet to be adequately explored. This study investigated academic and other potential correlates of task-unrelated images and thoughts (TUITs) during lectures. 463 undergraduate psychology students participated across three lecture sessions. During lectures, an auditory probe was sounded five times; alerting participants to record whether they were experiencing a TUIT at that moment. Results revealed significant negative correlations between TUIT frequency and age, detail of notes taken and course interest. Also, those seated in the front third of the lecture experienced significantly fewer TUITs. Furthermore, as TUIT frequency increased, there was a trend towards poorer performance in course examinations, which measure the learning of lecture-based content.
Source: “Daydreaming and its correlates in an educational environment” from Learning and Individual Differences, Volume 21, Issue 2, April 2011, Pages 158-167