Well, the point that abstinence doesn't protect against STDs is well-taken. The "alternative things" teens can do that don't count as "sex" (including the four or five varieties of acts known as "sodomy"), which in my experience are regularly relied on by young lasses wanting to keep both their "virtue" and their boyfriends, certainly can transmit STDs. Some are even more efficient means of transmitting STDs than sex is (anal intercourse, for instance). Of course, whether these things fit the Christian Coalition's definition of "abstinance" is a whole other question.
However, I am extremely dubious to your assumption that teenage kids don't understand this stuff and that schools don't teach it.
Of course no one in tarnation would have ever talked me into performing any of those acts with a condom anyway.