My son Adam went to Mike Douglas' camp at Whistler in June 2002 at age 17. For 90+% of the participants they spent the whole six days just on 2 skills: rail slides and 360's. Adam has excellent balance and expert skiing skills, but the parks also require acrobatic skill, like gymnasts and divers.
The results: Adam can do simple straight rails, but not slanted, curved or kinked ones. He was very close on the 360's but never had a clean landing. He's bought used twin tip Salomon 1080's so he can do 180's routinely and maybe work up to the 360's eventually. With regard to straight airs Adam can go much bigger since attending that camp. Douglas taught them to extend to "pop" the takeoff but stay in the compact form while in the air to maintain stability, then extend again before the landing to absorb it.
Adam said the camp was quite physically demanding. It's 3 days on, one rest day, then 3 more days, and he definitely needed the rest day. Other instructors included Shawn Nesbitt, Sarah Burke and one of the "3 Phils" from Quebec.