Last-minute swotting for an exam before going to bed might be a good tactic for students, according to new research on the benefits of "sleeping on it".
Sleep almost doubles the chances of remembering previously forgotten information, scientists found.
They believe it makes memories more accessible and sharpens our power of recall.
Volunteers taking part in a study were asked to remember made-up words either before a night's sleep or after 12 hours of wakefulness.
The "sleepers" were much better at recalling the words than the participants who remained awake.