One must read carefully before taking or rejecting the claims of such studies vociferously, but there’s a general point that can be extracted from news about a slowing down of the decrease of sexual activity among teens:

The latest figures renewed the heated debate about sex-education classes that focus on abstinence until marriage, which began receiving federal funding during the period covered by the latest survey.
“Since we’ve started pushing abstinence, we have seen no change in the numbers on sexual activity,” said John Santelli, chairman of the Department of Population and Family Health at Columbia University.

Whether or not the reporter’s calls for comment are what triggered the “heated debate,” it seems to me that Professor Santelli’s presumes too much. To wit, by what measure are we “pushing abstinence”? A handful of programs are available, mainly through churches and social organizations (rather than, say, public schools), and all of the accounts that I’ve read have described programs of limited duration — a few hours over the course of a semester or so.
Santelli’s claim is a bit like the protestations of a man who fears bathing that a little bit of soap spilled on his toe didn’t make him clean.