This topic has been discussed in several threads. I believe the researcher who disproved the effect of Virginity Pledges started with the premise that the original results showing the pledge worked was not accurate because it did not compare similar subjects. In other words in her study only by comparing teens who had the same values and outlooks on life could a valid conclusion be drawn.
To her it was no fair putting committed Christians who believed sex was for marriage only in with a bunch of teens who were just making outward gestures without any inward morality to bolster those gestures into promises.
So the whole argument virginity pledges do not work is wrong. They work when the person making the pledge has the inner character to believe in what they say.
Christian, Christian In Name Only, atheist, or “whatever” .... most girls give it up before marriage.
The Virginity / Chastity / Good Girl Pledge shouldn’t have been tried on the general population, simply because it won’t work. It requires a moral, spiritual, and community framework that simply doesn’t exist for most teenage girls.