Students who study hard all week and party on the weekends may lose a lot what they learned. Sleep deprivation on critical nights after learning may cause a 30% loss. Carlyle Smith, a professor of psychology at Trent University in Peter borough, Ontario researched the effect of sleep deprivation on learning by controlling the sleep of students the night they were taught a complex logic game and a list of paired words.

Smith found that when students were tested on paired words, a week later there was no learning deficit among the students deprived of sleep, but when tested on complex logic game, the students deprived of sleep showed a 30%
learning deficit when compared to the group of students not deprived of sleep.
Sleep deprivation on the 3rd night after learning had the same results showing a deficit of about 30% for the complex logic game. Sleep deprivation the 2nd night after learning seemed to have no effect.

This means that if you party all night on Friday after a rough week in the school you will lose 30% of the learning you acquired on Wednesday and Friday. If you lose sleep on Saturday night then Thursday's learning is also affected.
Ref: Mathematics today