I went in 8th grade, which was like 9 years ago. I did the Epcot program. All I remember is that we had a tour for half the day and the other half we were on our own. For the tour, I remember going underground (I think it was underground anyways...we entered somewhere in innoventions I think) and seeing the computer control room and learning about the science of making all the rides go. We saw the old systems that (at the time) were being phased out and we saw the "new" (at the time) systems. I remember learning about the plants in The Land. And I remember going inside Wonders of Life, particularly that we went in the room with the simulators for body wars and watched the simulator itself move, which was cool. And I remember riding Horizons like a million times (we originally just wanted to see all 3 endings, then we kept going back and taking turns picking endings).
I found the YES program to be quite fun and was and am very glad that I took part in it. I really think it's worthwhile, if you're given the opportunity. I hope my fragments of memory from my experience help give you some of what you're looking for.
After looking at the above link, it appears that the session that my class participated in was the Synergy in Science program. Unless, of course, they've changed the programs since my middle school days.
