Depending on the type of the pen I'd say either buy a new one or go to school more often. I use your everyday mechanical pencil 6 hours a day and I can take it apart and fix any issue within minutes.
I actually got it yesterday at like 10:45 PM.
But, being the idiot I am, I bought lead with it and tried to put it all in at once, thus forming this topic. And my pencil's clusterforget
EDIT:
Okay, take the eraser off, then shake it up and down a LOT. Like, really hard.
No luck, it's jammed in there, but I can wiggle it and it snaps back to place.
EDIT2:Also, there's about 9 pieces in there.