You can dream the thing's you've got for school! Like, if you've got Maths, you dream you do an excersise in the class:
x-7345=42501
What's x?
42501+7345=49846
x=49846
Science: You can do some experiments.
History: You're the person it says! Or just you are a teacher teaching the lesson (xD)
P.E.: Play whatever sport you like!
And so on.
Since a regular sleep is 6+ hours, it'll be like School!
Although you may get sick of 12 hour school
But think it the other way: It's the school that you're able to control!