It is no secret that the children of certain families (and we all know who we are) are primed to take a disproportionate share of the places at the best—or at least the most prestigious—colleges. That's because we're already sending our kids to the kinds of excellent schools that help prepare them for admission to such colleges.

But just in case our children don't quite have the stats to make it into, say, Georgetown or UNC on their own steam, you can bet that we, as parents, will do everything in...