In the progressive/traditional discussion, I've always felt that kids from well-educated homes can be successful in either. To the extent that either model falls short, parents pick up the slack at home via enrichment or tutoring. However, at a certain point, I would think that there must exist schools somewhere that are able to provide adequate education, but it seems even at TT there is an acute need for tutoring.
Not all children learn the same. Some children will do better in a progressive, project-based, inquiry type environment and some will do better in a more structured, traditional environment. It's not only driven by the type of home from which they come -- it's also driven by their personalities, learning styles, attention spans, etc.