Cannot speak to Skip Barber's school personally, but I can speak to the track. I think it is a very fun track and I have driven there many times. Road Atlanta is a fast, difficult track at the amateur level; it has lots of elevation changes, and by today's standards, not much runoff room. Turn 12 has a high pucker factor and if you early apex there, you are in real trouble. I balled up a Z06 there, too, on the inside of turn 1-2.
Interestingly, RA has probably been rendered nearly obsolete by the ALMS P1 cars. They have so much aero downforce that many of the curves that are a challenge for us are a walk-in-the-park for them. I have seen the P1 cars pass slower cars on the way down turn 12 on the wrong line and the drivers don't even seem to lift. I am always amazed there aren't more wrecks between the P1 cars and the GT cars at RA as the speed differential is substantial.
I did the advanced two day racing school at Road Atlanta a little over a year ago. Actually, I've done the two day school several times (at different tracks) because the number laps you get per dollar is actually better than for a race weekend. As for Road Atlanta, it's a great track to drive. Truly one of my favorites. Regarding the two day high performance school, from what I've heard, it is a bit like their three day racing school in that they will spend time teaching you racing basics (heel-toe, threshhold braking, racing line, etc.) while also letting you try several high performance cars. I can also say that the instructors that I've had for the racing schools and regional races have been absolutely top notch. I'm sure you will enjoy it.
I did the 3 day racing school there a few years ago in their formula cars. I echo what others have said. Top notch instructors. Fun track although the first time I went under the bridge and then down the hill towards S/F, I figured I'd never go any faster -- it was a "thrill". Of course I was wrong and by the end was flying over that hill into the blind turn.
Not to scare you but, drive within your limits at Road Atlanta. I watched a guy bite it pretty bad through the 3-4 complex of turns. He seemed to just take it too fast. See attached photo. The great thing about Skippy is you pay a deductible and their insurance covers the rest. Still it was an expensive, embarrassing, and a bit painful experience for the guy.
i drove RA with panoz and it was great fun for an amatuer driver. the esses going uphill are great for testing your finesse and 10-12 will test your balls. if you bring your own car, you'll be fine. if you drive anything with bad visibility over the hood (panoz, viper, mustang), dropping down 11 into 12 can be a little spooky.
it's memorable, like turn 17 at sebring. if you're not nervous, you're not driving fast enough.