I have been thinking about something that you could do to make it fun for the 4th graders, and I think I just came up with something...
How about a treasure hunt using math for the clues...
I don't have the whole idea figured out, but how about you start the event by handing each child a piece of paper. The paper has locations for each "rest stop". For example, the question might be...
1. What is the square root of 484
A) 19 - Go to the art room.
22 - Go to the Library
C) 34 - Go to the gymnasium
D) 12 - Go to the playground
At the different destinations you could have either a "You answered the question incorrectly, this is not the correct location!" or "Good job. Now which of the following numbers are not evenly divisable by 6? Then have a new set of answers with different locations.
The final location would be the cafeteria, or wherever you start from. The first one to complete the hunt and show how they figured out the answers wins something, like a WebKinz (the kids are crazy about this right now...)
You could make it that instead of sending them all around the school if they got the answer incorrect, they instead pick a card for the answer they believe is correct. Once everyone is back they turn in their cards and a time is recorded. The one that had the most correct in the fastest time wins...
I'm sure there are many different ways to do something like this, but the general idea is there and would be pretty fun.
Let me know what you think.
Have fun.
PresidentJim