There are different opinions and values on when, or if, a teenager should engage in sexual activity. If they do, they need to know how they can reduce the risks of their OWN choice, which can be provided by a comprehensive sexual education program. If saying no doesn't work, you need to know how to deal with what comes next.
The thing about teenagers is the fact that they are young adults with their own thoughts, minds, and feelings. Some are exceptional while others make really poor decisions. It would seem that those who make poor decisions are often times misinformed by either peers or their parents. Forcing a teenager to do, or this case not to do, anything is akin to moving the mountain to Mohammad. With today’s technology and over exposure to media of all types, it is virtually impossible to try to talk a teen into the fact that abstinence is probably the best idea when the world is telling them otherwise. As the old saying goes, “Curiosity killed the cat”. Therefore, it would seem that the best option would be to educate them in all the possible consequences, and allow them to make their own choice.
This one is by far better than abstinence. The main reason for this is that not a whole lot of people do not abstain from sex and then they do not know anything. At least if you teach the kids what they need to know then they can be safe if it ever happens.