I'm still a student also, and last Friday I finished my clinicals with first graders...I got them all stickers (I found little 15 cent sheets of Mrs. Grossman's stickers that they LOVED!). I'm not sure if your 4th graders are too cool for that, but my kids were loving it. You might also be able to find some really cool pencils or pens for cheap that they'd like...they have some sparkly pencils out now that seem to be all the rage. I've also heard of people getting a copy of a class picture, and giving one to each child with a special note. Hope that gives you some ideas!