Ugh. Also read as: "Something I haven't seen doing something I don't expect it to? Ridiculous!"
The correlation between students at Waldorf schools and prestigious schools later is extremely easily explained by a single character: $
That said, something different than our current, standard public-school fare probably stands a decent chance of doing better. Anything with more attention to the methodology stands such a chance. But I'd be willing to bet that many of the successes also simply reflect parents that are more aware of their children's education.