Since I live in NZ I looked at how schools here teach about sex and reproduction. This website is for parents' information, and I think it does a good job of explaining clearly that what is taught is always age related, and that parents have a right to be consulted. Extract below:
Do schools have to consult with parents?
Boards of trustees have to consult with school communities at least once every two years on their draft health curriculum. This includes how the school will implement health education, including sexuality education.
This is your chance to ask questions, share your ideas, and express your views about what you would like to see happen in this part of the curriculum.
How the consultation happens is up to each school. After consultation the school’s board will approve how the health curriculum will be taught.
On respecting different beliefs:
Will my culture, religious beliefs and values be respected?
There’ll be a range of views in your community about the place of sexuality education, some of these will be based on culture and, or religious beliefs. Schools try hard to respect differences in culture and religion.
If you are concerned about sexuality education, it’s important to talk to your school first. Your child’s teacher may not know about your beliefs, or the things that are important to you, so make sure you tell them. If you’re still concerned, talk to the principal or contact your school’s board of trustees.
You have the right to withdraw your child from particular parts of sexuality education by writing to the principal
I imagine that this is the kind of sexual education programmes that UK schools teach, with consultation with parents before implementation?
parents.education.govt.nz/primary-school/learning-at-school/sexuality-education/