What you need:
Handheld (not car!) GPS receivers – I like the Garmin etrex Venture HC. It has a colour display, geocaching mode, it’s very durable, waterproof –ish (rain is fine, but don’t drop it in a pond), and it’s bright yellow. The kids have a harder time misplacing something that is bright yellow! I have 6. With 27 students this breaks down to 4 or 5 in a group.
Caching containers! I’ve written about some creative containers here. The standard is just a plastic container, either spray painted or with camouflage tape (shop in the hunting section – it will be there!) to blend in to the surroundings.
An idea for clues. Each cache has to have something in it for the kids to collect. This is where you can tie geocaching into almost any subject. Last week I had colour coded clues to Canadian Animals. Each cache had six coloured pieces of paper in it. If you were the yellow group you collected each yellow clue and tried to determine what animal you had. Each group had a different animal. I’ve made caches full of money, with a decimal problem on the lid. The students had to solve the problem and bring the answer back in money. I added baggies to the clipboard to keep them organized that day.
Once you have clues in all of the caches you are ready to go and hide the caches around the school yard. This is the fun part. I often get students from other classes to come and help me. You would be surprised with the creative places they come up with.
I use mapping topographical mapping software (a very simple, user friendly version comes with most GPS units) to download the co-ordinates to the computer. Then I plug in the other five receivers one at a time and upload the co-ordinates to each one. It takes about 5 minutes to load to all of the receivers.
I set up groups for the students. Each person has a job, and they rotate each time we go out. They each get a chance to be the navigator (use the GPS), photographer (use the camera), recorder (track clues on the clipboard), and clue opener/replacer (open and put the containers back)