David Leonhardt:

ASK just about any high school senior or junior — or their parents — and they’ll tell you that getting into a selective college is harder than it used to be. They’re right about that. But the reasons for the newfound difficulty are not well understood.

Population growth plays a role, but the number of teenagers is not too much higher than it was 30 years ago, when the youngest baby boomers were still applying to college. And while many more Americans attend college than in the past, most of the growth has occurred at colleges with relatively few resources and high dropout rates, which bear little resemblance to the elites.

So what else is going on? One overlooked factor is that top colleges are admitting fewer American students than they did a generation ago. Colleges have globalized over that time, deliberately increasing the share of their student bodies that come from overseas and leaving fewer slots for applicants from the United States.

Related: “Financial Aid Leveraging”.