In fact, it is counterproductive.

As today’s L.A. Times reports:

Young adults who as teenagers took pledges not to have sex until marriage were just as likely to contract a venereal disease as people who didn’t make the promise, according to a study in the Journal of Adolescent Health.

Why? 

"The study found that 88% of sexually active people who took the pledge had intercourse before marriage. Sexually active pledgers were less likely to use condoms the first time they had sex, Bruckner said."

Sex education programs that teach only about abstinence are "outside the reality of most adolescents and young adults," Bruckner said.

Fuck "just say ‘no’".  Let’s educate these kids properly, and keep the moral agendas out of it.