Lots of discussion on The Choice blog around this piece on a new practice test intended to prepare eighth graders for the kinds of questions they'll see on the PSAT and SAT.
It might seem logical that the earlier you start to practice anything, the better you're going to be at it. But there's enough stress surrounding college admissions and its accompanying tests without pushing the prep down to the eighth graders.
We've worked with lots of high school students with great test scores who were admitted to selective colleges. But very few of those students got those results by starting their test prep in eighth grade or earlier. In fact, a lot of students who've been vigorously prepping for years suffer because of it. They've spent more time practicing the SAT than they have playing in the jazz band or writing poetry or singing in the school musical, all of which are better for kids and just as important if not more so than test scores.
Test preparation has its place, but I would never recommend that a student start earlier than the sophomore year. In fact, most students who prepare during their junior year (or the summer before it) are able to get good results if they put in the effort.
It's never too early to begin preparing for college, but it can be too early to worry about standardized tests. Tell your pre-high school kids to read, to work hard in school, and to develop their interests. All of those things will lead to better overall results and happier kids than early test prep will.