Just my 2 cents …

(1) Ideally you’d divide 40 people into at least 4 groups/teams, more if possible. Having 10 or more people heading to the same thing, in my opinion, will be a bit crowded.

(2) This means that ideally you’d have 4+ leaders that know how the GPS units work.

(3) I recommend that you DO pre-program the coordinates … with that many people, you’d have a tough time “teaching” how to punch in coordinates … focus your efforts on the “fun” of finding caches not learning exactly how to work the GPS units … besides there are so many different brands/models, no two are done the same any way.

(4) From personal experience with a group of kids about half that size … don’t get long winded with a speech before hand about geocaching and how it works. Give them maybe a 2 or 3 minute summary of what it is your about to do. I learned the hard way that about half your audience will wander off mentally (or even physically), everyone will start getting noisey, and no one will hear the rest of what you have to say.

(5) If you can pull it off .. have each group go to different caches (even if some are temps). I tried to have three different teams do the same caches but in different orders, thinking they’d never meet up and bunch up … but in the real world, one team goes too fast, another team goes too slow, the last team went just right … and they all end up at the middle cache at the same time.