People see issues differently depending on how they are framed.
This article looks at framing in the abstinence debate, specifically how using abstinence as the subject of a sentence instead of adolescents takes away adolescents' agency. That sounds abstruse, but it's an important difference both for advocates and sex educators (including abstinence educators.)
That is, saying "Abstinence is the only way to 100% prevent STDs and pregnancy." puts abstinence as the main idea, rather than adolescents, and makes the statement needlessly abstract. Adolescents thinking about having sex themselves would probably not feel any personal identification with that statement even while accepting the statement logically as a correct proposition.
Likewise, they don't use this example, but I think it applies equally: statements of "should" such as "Adolescents should wait to have sex." also take agency away and simultaneously add moralism, which is easy to tune out.
The article proposes using language that put adolescents back in the agency role, "Waiting to have sex..." or "Deciding not to have sex..." I like the statement with deciding best because it emphasizes the choice aspect.
I am not sure that framing would change efficacy of a curriculum, but the qualitative research from a couple months ago about adolescents' sexual decisions does indicate that the first two phrasings are probably ineffective, so it wouldn't hurt to try.
And there is no reason the abstinence movement couldn't adopt this wording. Everyone knows that adolescents have agency over their sexuality --- at the end of the abstinence program, they will be making decisions, not passively following rules. Adolescents who intend to be abstinent need to make decisions about intimacy, and in fact their decisions are more difficult if they want to be effective. Decisions have to include complete and accurate information which requires teaching birth control accurately.
There are certainly some sex-positive books written for young evangelical adults that emphasize their agency; one even says that sexuality is part of every social interaction ("Soul Virgins" written by two evangelical sex therapists, reviewed here earlier). I haven't seen any sex-positive literature for teenagers, but that doesn't mean it doesn't exist. Many of the adolescent curricula that I have seen do talk about sexuality as a contaminating external force, and that's just not productive.
The abstinence movement has other models for sexuality, such as sexuality as altering relationship development, that while negative don't mark sexuality as bad, but just as out of place in an adolescent relationship, and do concur with the mainstream adolescent research. So many of my colleagues begin papers by citing the statistic that most adolescents who have had sex wish they'd waited and that younger people are more vulnerable to STDs. (This American Life even has a segment about how couples use sweet talk to avoid being in the moment and developing their relationship. And last night the Big Bang Theory featured a girlfriend using sex to avoid uncomfortable conversation.)
These models of sexuality require discussions about how to develop healthy and meaningful romantic relationships. That's more difficult to teach than moralism and threats, but has some chance of being effective.