They're in college, according to an analysis at Girl in the Locker Room.
The theme that men aren't going to college has seemed a bit suspicious to me all along. Assuming Girl's reporting is accurate, more men and women are going to college than ever before, both in absolute terms and as a percentage of the college-aged. It's just that women have really increased their percentage of attendance, wherewas men have only somewhat increased it.
This is exactly the same argument that I tend to use in fighting with economically illiterate leftists - it doesn't matter that Group A's income is growing faster than Group B's, if both A and B are both making real improvements. Envy is stupid; equity is unattainable; improvement is the real metric.