For middle schoolers, I put preparing for the SAT right up there with driving and voting–they'll do it someday, but it's much too early now.
Still, there are some productive measures parents can take with their middle schoolers to prepare them for college, and Jay Mathews offers up eight of them here today.
And if you don't mind a few instances of advice-overlap, here's my July 2010 post with college admissions advice for 6th, 7th and 8th graders.