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.
Do not forget that most teenage boys are also not reared in such a framework.
And in a lot of cases, the moral/spiritual framework consists of ludicrously protective parents/community. If you get outside the very protective church/community/etc., problems start to show up.
The main problem I see with these types of pledges is that they basically say "Sex before marriage is bad. God doesn't want you to do it. So don't." and don't really address any of the underlying issues. No one ever mentions that sex and love are often two entirely different things (although they *are* meant to go together, humans tend to fail at that), or that women have a sex drive. So, when confronted with a horny boyfriend who says "You'd do it if you loved me" and the raging hormones that they're not supposed to have, they fold very easily, regardless of whether they're mentally/emotionally mature enough to handle the situation.
The people that have the most success saying 'no' until they're ready (after marriage/college graduation/whatever) are the people who have had the reasons besides "God doesn't want you to" explained to them in a reasonable, adult manner and have been raised to stand up for themselves. Unfortunately, the latter isn't very popular among parents of girls (they're supposed to be sweet and quiet and fit in, dontcha know), so even the explanation doesn't work all the time. Then, the only option is being incredibly vigilant in sheltering your daughter, but that leads to it's own problems... I'm honestly not sure which one produces more messed up people: the sheltering or the sex.