I really like the idea of a geocaching club. Several years back I developed a program for Eckerd Youth Alternatives, Inc. at camp E-Sun-Alee in Deer Lodge, TN. The teachable opportunities during geocaching activities are endless. Below is some of what I did.
1. Teach a bit about map and compass reading. The Outward Bound has a book which is written for students at the high school level. The Outward Bound Map & Compass Handbook can be purchased from REI for $12.95. I used Microsoft Publisher to create a simple brochure which included a lesson on map and compass reading, and a short quiz to test the student's understanding of the information.
2. Cheap GPS units! My company currently uses the Garmin eTrex. This unit is no longer being produced. However, you can purchased refurbished units for less than $70.00 from MegaGPS. You can download a quick reference guide for most Garmin unites online. I had several of these quick reference guides laminated, so the students could take it along during geocaching activities.
3. We used geocashing as an opportunity to teach some of the guidelines of the Leave No Trace (LNT) program.
4. Several of our facilitators later attended Project Wild courses which greatly expanded our reach and purpose.
Feel free to shoot me an e-mail if you want to discuss these ideas in more depth.