Thanks everyone for your help. I was pretty certain that WAAS was indeed a signal correction process, but now I know exactly what it does. I ended up ordering the eTrex Vista, but while I was shopping for the device noticed that no one listed signal averaging as a feature. Not that its a terribly important feature because I knew that you can always walk away from a WP and then back again to verify your results.
My son should be able to head out this weekend with the Vista and compasses in hand and I'm really looking forward to it.