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).
If you state the abstinence is on the ONLY way to be completely safe, than are you not injecting morality into the school? Unless you plan on telling people no sex EVER no matter how long you live, then you must teach an accurate, balanced sex education – including information about contraception and condoms, as we've seen from studies that abstinence programs fail. Abstinence programs are not effective at delaying the initiation of sexual activity or in reducing teen pregnancy. People generally start having sex around the same age around 18, that's the average from 44 countries (US included) so you must teach about sex BEFORE 18. Given that 18 is the average age of someone's first sexual experience it is safe to say that some people have sex much younger, therefore we should be teaching about sex when student are 13 or 14 years old (think 7th grade). You can truthfully say abstinence (no sex) is the safest, but that doesn't prepare student for real life, almost every child is the result of sex, and would you rather student find out that sex can lead to babies before they have sex or after? Or would you rather say "The only sure way not to cause a pregnancy is not to have sex, but if you have sex this will REDUCE your chances of causing a pregnancy." With many abstinence only programs many teen choose not to use contraception, after all buying any form of contraception, means you're going against the abstinence program or that you are going to violate your pledge, that many abstinence programs as students to take.
Teach and leave morality out of it.