The school will usually know when to give sex education. Of course, there is some difference among schools, on when the subject is taught.
Sex education is not an invitation to indulge in sexual activity. Rather, it is scientific information given at the level of the students understanding. As their bodies become sexually mature, children will be self conscious and not be sure whom they can safely consult to check out if their development is normal. It is good that the teachers in the school talk to them about it, warning them not to let anyone abuse them. If the children do not get the information directly in school, they will try to find out from magazines and the Internet.
In my view, the schools should also tell them the risks of pornography, which is available on the net. Parents should also know what has been said to the students and they must ensure that they put a lock on unsuitable sites on the computer. Parents must also be clear and candid when asked questions by their growing children. Knowledge will not result in sexual indulgence.
A certain amount of concern on the part of teenagers about their body and their looks is totally normal. Instead of acting like policemen, parents would be well advised to have a light touch and a sense of humour in dealing with their children. Respect them as individuals and try and remember your own experiences of growing up. Be firm and be affectionate.