I have two sons, and homeschooled both of them. Both have autism-spectrum disorders, the older one has high-functioning autism, the younger one has Asperger's Syndrome. I mention that because people with these conditions require direct, concrete information in order to learn. Euphemisms and implications won't work - they just don't get it. Since they were homeschooled, the "school versus home" issue never arose.
Over the years, my wife and I answered their questions, but they really didn't ask that many. We took opportunities to teach them about sex and reproduction as situations arose which made it an obvious topic (the birth of a cousin, etc.). We also brought up information that they should know, but may or may not have been ready to understand. Parents do this all the time with manners and religious beliefs, so why not sex and reproduction? When they didn't understand something, it "rolled right off their backs", and we knew we would have to try again later. A good example is Nova's "The Miracle of Life", which I showed them once or twice a year. The details of prostate and Fallopian-tube anatomy went over their heads when they were young, but the mom giving birth to a baby at the end always held their attention. Every year they learned more from the video.
As part of their homeschooling, I included materials on sex, beginning with some "where did I come from?" type books, and proceeding through the "facts of life" books for pre-adolescents and teenagers. As with all their educational materials, I was careful to read through them thoroughly, not fearful that they would "say and show too much", but concerned that they would contain errors and perpetuate fallacies, which they often did. Any such book promptly went into the "donation" stack for book sales. The few that I kept were from secular sources, but I always taught them from a Christian perspective.
I taught them the honest, unembarrassed facts about the anatomy and physiology of sex and reproduction, the correct medical terms for the organs of both sexes, the fundamentals of pregnancy, birth, the menstrual cycle, sexual intercourse, and sexually-transmitted diseases. Birth-control information emphasized the difference between contraception and post-conception termination, and why that difference is important. We talked about masturbation, not in an accusing manner, but just facts. We also covered the many "variations" in sexual behavior, and their moral implications.
I think it's important for parents to specify some boundaries, such as "what your mom / dad and I do with each other is none of your business". This frees the parents to discuss many topics that should be discussed without the implication that they have personally experienced them. Likewise, it's helpful to tell your kids that you've gathered sexual knowledge from several sources (books, websites, friends, etc.), so they don't think your knowledge comes only from personal experience.
Throughout all of it we emphasize the Christian and Biblical perspectives, and try to avoid the societal myths and values which contradict these. Contrary to popular opinion, sex education and Christian education concur much more often than they contradict. An example I've used with my kids is: "God is gracious and loving. He gave women labor pains in the curse, but He also gave them multiple [bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse][bless and do not curse]"
My kids are 22 and 19 now, so it's been a while since I've browsed around in Christian sex-ed materials. Many of the ones I've seen are great on the moral message of sex within marriage, but I find them lacking in detailed, realistic illustrations and / or photographs of the human body, and the genitals in particular. It seems that even the best materials retain the fear of being mistaken for pornography rather than to simply and clearly show what they're trying to teach.
