Livescience has a great article about whether or not pledges work. They use violence and abstinence pledges as examples. Their conclusion is that they don't work. Big surprise there.
One thing I found interesting was that "one study found that almost 90 percent of them broke their vow [of abstinence]". There is so much evidence out there about how abstinence doesn't work. I think it's time to move on and start offering campaigns on protection and smart choices.
Violence and Virginity Pledges: Do They Work?