In order to do this, a professor would want to use either a fixed ratio schedule or a variable ratio schedule. These would be more useful than fixed or variable interval schedules since both of the ratio-based schedules are meant to elicit high and steady rates of the desired response (studying).
A professor might do this by rewarding students with a positive grade every time they complete a certain number (fixed ratio) of sections or chapters of their book. This would make students eager to complete that number so as to get the grade. Alternatively, the professor might give the grade at random points. The professor might sometimes give the grade after one unit has been completed while giving the grade after three units at other times. Either way, these schedules would motivate students to do their work steadily because they would either A) know they had to finish a certain number of units to get the grade or B) want to complete another unit in case they would get a grade for it.
Of course, the professor would have to give grades that were high enough to be motivating. The professor would also have to be satisfied that the students were actually doing the work. But if these conditions were satisfied, the fixed and variable ratio schedules would work best because they elicit more frequent and steady performance of the desired response.