Sex education is one of those things that is too important to leave in the hands of the family unit. I know many people who got bad information, or simply no information from their parents about the "facts of life" - the result of this information deficit is real and costly. Unwanted pregnancy, high rates of STD infection, and sexual abuse/violence are all side effects of restricting information about sex. As difficult as it may be for some parents to accept, all young people deserve facts and knowledge about how to conduct themselves sexually, and what the consequences of their choices will be.
Sex education absolutely MUST be taught in schools. It is one of the most effective methods we have taken advantage of in recent history that has had a direct impact on the number of teenage pregnancies in the USA.
Sex education from biological/informative point of view is fine. Also important to teach that abstinence is the only way to be completely safe. I am also a proponent of teaching objective morality and justice in school, but that has classically been seen controversially. I think it is important that it is taught in school, although I feel like parents have a much greater responsibility in the issue. Of course there are things that the parents haven't been taught that the schools will do better. That is why it is so vital that it is taught in school. But schools should not be promoting a particular mindset or approach (and if they do promote one, I think abstinence is the healthiest and most responsible option to promote, even if it is taught alongside contraception).
Abstinence equals teen pregnancy and STD transmission because teenagers are going to have sex even if you tell them not to. You might as well teach them how to do it safely. Teenagers are naturally rebellious so telling them not to do something will make them more likely to do it.