You can find good local programs by asking around at outdoor-gear stores, bike shops, and ski hills. For top national courses, here are the best.
ACTION/SNOW SPORTS Windells Academy (windells.com), near Mount Hood, Oregon, is where Shaun White first learned to do a cork 540. It now offers skateboarding, BMX, and freestyle snowboarding and skiing programs. Dave Murray's Summer Ski and Snowboard Camps (skiandsnowboard.com) have alpine racing programs in addition to freestyle camps.
WHITEWATER Northern California's Otter Bar Lodge Kayak School (otterbar.com) offers a NQGU (not quite grown ups) Kayak Camp in the last two weeks of July for 10- to 14-year-olds. In North Carolina, Nantahala Outdoor Center (noc.com) has been churning out Junior Team, U.S. National Team, and Olympic paddlers for nearly 40 years. There are programs for kids as young as nine.