Read all about it. Andrew Brown.
Mark Regnerus, a sociologist at the University of Texas in Austin, conducted a survey of 3,400 American teens from which it emerged that white evangelical Protestants have sex younger than any other religious group but black Protestants. They are also less likely to use contraception than other groups, especially secular ones.
Other sociologists turned up some fascinating facts about the “purity pledge” movement, an occasionally creepy attempt to get teens to pledge themselves to virginity until they marry. It does, sort of, work for a while: it seems to postpone sexual activity for 18 months on average, and when I was a teenager that would have seemed several lifetimes. But this only happens when the pledgers are a minority who can feel themselves superior. Once the proportion of pledgers in a school rises above 30%, the success rate for all of them shoots right down (or up, depending on how you count).
The New Yorker has the story.