Define Responsibility When It Comes to Your Children and Sex
In order to alleviate the uncomfortable topic of sex with your teenager, you can start talking to them about it when they are much younger. If you begin to define responsibility around this issue early on, it will never become an "issue" in the first place.
I am amazed about how much parents balk at broaching the subject of sex. My first order of business would be to take a good look at my own hang ups on this matter before I sat down to discuss the subject. If your kids see you all weird about discussing sex, they will take that away from the conversation, and not understand what you were trying to communicate. The Internet is full of funny mistakes parents make when discussing this topic. You won't be perfect at it, but you don't have to be all hung up on the topic like it is a tabu subject, either.
You may decide to let the school handle sexual education for your children. Wrong
It is ultimately your responsibility to supplement the teachings of the school system with the family's beliefs regarding the subject. The school may be teaching values along with the basics-STD's, protection, etc-that you disagree with. Teen pregnancy is on the decline in the U.S., so someone's doing something right, but don't expect other's to take the responsibility for teaching these values to your kids.
Along with the basics, you'll need to discuss peer pressure and answer any questions your child might have. If they've gotten the wrong information on the playground, you're going to want to know so you can right it, and they are not going to talk to you if they can't trust you. So do not approach this topic with a negative attitude, and don't tell them stupid stuff that isn't true. None of this "stork" talk. You need to tell them the truth using the proper medical terminology the first time they ask a question about where babies come from; I don't care how old they are. You need to discuss it at their level, for sure, but outright lying because you are embarrassed is one of the best examples of bad parenting that I know.
If this sounds incredibly difficult, well, it can be. No one said raising children would be easy. You've been able to define responsibility on other subjects up to this point, so be prepared.