Have you looked into the Science Center's Science Blast Camps?
http://www.slsc.org/Just4Kids/SummerScienceBlast.aspx
My DS6 went last year and was very upset that he couldn't do that year round!

If you / your kids are up for overnight camps, I've heard wonderful things from my HG niece about Cub Creek Science and Animal Camp (www.bearriverranch.com) in Rolla.