Some time ago I came upon this editorial in AAAS's Science magazine: The lower your social class, the ‘wiser’ you are, suggests new study. As always, it's best to go to the source and not rely too much on "second-hand" editorials but we'll do without for now.
The article is on open access here for the interested.
First of all, what is wisdom? It depends on whom you ask. Something that might approach a shared understanding would be to define it as state of being that incorporates thinking and acting in a manner that is appropriate to the situation at hand, for the simultaneous good of the self and of the other, according to learned knowledge and experience. Something like that. A shorter definition would be: the opposite of being an idiot (or an asshole).
Anyway, that's not the subject of the article. Apparently here wisdom is defined as the capacity of understanding the situation of other people and to think/act accordingly as to avoid useless conflict. The abstract of the article reads "wise reasoning (recognizing limits of their knowledge, consider world in flux and change, acknowledges and integrate different perspectives) in interpersonal situations".
The findings are fascinating (and fun).
First of all, it doesn't depend on the IQ.
Secondly, it seems that growing up in a working-class environment provides the individual with a "higher wisdom reasoning" when compared to those individuals from "the middle class".
Now, where the author makes a mistake is when he supposes that people in the middle class want to pursue education to improve their IQ. This is wrong. Education (especially self-education, not at school and university) can eventually preserve the IQ from degenerating, it doesn't work like that. And besides, IQ is independent of wisdom as emphasized before.
It is safe to assume that it is a developmental issue that affects children and adolescents in those "middle class" environment,where they are not given the adequate social environment to develop their social skills. Play and social interaction are very important for the development of a grown-up individual, and as this article kind of demonstrates, for his or her wisdom.