A doodle in the margin has ruined more lectures and started more careers than anyone admits.

The part of your attention that wanders off during fourth period is the same part that makes things. It is not two traits. It is one trait sending two different bills: the lecture you missed, and the thing nobody assigned you that you built anyway.

Do not try to kill the drifting, because you will lose the useful half with it. Give it somewhere to go. A back page, a bus ride, twenty minutes after dinner where wandering off is the actual assignment.