I just did a google search on "intellectually challenged" (with quotes) to find out wether it's the polite way to say dumb and this turned up third.
Heh, bad choice of wording. Had they said "Challenged Intellectually", it would be perfectly clear. Too many connotations the other way though.
Methinks they should have gone with "stimulated" instead of "challenged". (Note that this only works with "intellectually". Had the original text been "be physically challenged", we'd have another WTF on our, um, hands.)
It should be "Challenged Intellectually" if you don't want to split the infinitive verb. Putting 'Challenged' first shifts the emphasis the right way in this case.