Though there’s considerable overlap between the two big social-networking services, only one usually becomes the center of a teen’s online social life. Most often the choice is made depending on where your friends are. But what determines whether clusters of friends alight on MySpace or Facebook? A controversial answer comes from Berkeley researcher Danah Boyd: it’s a matter of social class.

A few weeks ago, Boyd—who has done extensive ethnographic work on online behavior, posted an essay sharing her (admittedly nonscientific) findings after months of interviews, field observations and profile analysis. Generally, she contended, “The goody-two-shoes, jocks, athletes and other ‘good’ kids are now going to Facebook. These kids tend to come from families who emphasize education and going to college.” MySpace is still home for “kids whose parents didn’t go to college, who are expected to get a job when they finish high school.”

It’s also, she says, the preferred digital hangout for outsiders—burnouts, punks, emos, goths, gangstas and minorities.

Boyd does concede that a lot of this may have to do with the fact that Facebook began at Harvard and spread out from the Ivies. But she believes that there’s conscious self-identification involved in the choice.

Facebookers are strivers; MySpacers are there in part because they’re rejecting the values of preppies, jocks and tools.

Boyd’s essay triggered a firestorm of criticism. Facebook was too cool to comment, turning down my request as abruptly as a cheerleader nixes a nerd’s prom invite. But MySpace founders Tom Anderson and Chris DeWolfe were eager to dispel what they considered a wrongheaded take by a researcher they respected. For one thing, the sheer number of MySpace members (many of whom are also Facebook users) makes it hard to talk of a divide: “How are you going to put 70 million people in a box?” asks DeWolfe. (Facebook has 28 million.) He also notes that class has nothing to do with all those who access videos and music on MySpace. (Boyd says she’s focusing on which one teens use for their core socializing.) Anderson adds that people go to MySpace for the freedom to design their page the way they want it, while Facebook’s more-stringent template enforces a spartan design ethic. Boyd argues that upscalers like Facebook’s clean style, while the nonelites prefer the blinglike cacophony that is MySpace. As Boyd writes, “The division around MySpace and Facebook is just another way in which technology is mirroring societal values.” If she’s right, the Facebook and MySpace debate will be more than a choice of online destination. It will be a hard look into a societal mirror.