As everyone else has said, lessons need to be age appropriate and whilst I appreciate that children probably know a lot more than we did at that age. I can't remember what I knew at age 9, but I'm pretty glad I didn't have to be imbued with some of the explicit material that schools have for such lessons now. However different days, different influences, I was still fully immersed in a world of Enid Blyton as were many of my peer group.
The testaments of various parents I have read, MN is always quite revealing as to what is being taught and the increasing somewhat covert nature of it of late, in that there isn't a lot of transparency, this is why so many parents are feeling a growing disquiet.
Whilst we know that kids now have a knowledge about all manner of sexual practices that our generation wouldn't have had a clue about, isn't that because of their exposure to pornography which is hardly anything to crow about, knowing the pernicious effect it has on an immature mind at a crucial stage of development.
As far as learning about the fairly extreme practices of anal sex and strangulation for example, I hope it would be in the context of shoring up young people's resistance into coercion in partaking in any practice that could be damaging or dangerous to them and to imbue them with the fortitude to say no if they feel uncomfortable or unsure about anything, particularly when they are at an immature stage or even on the cusp of sexual awakening. Being taught about extreme sexual practices in a rather glib, nonchalant way of "oh this is what some people do" could, well be extremely damaging to some, there's hardly a one size fits all as to a level of maturity reached at any age, and parents should be consulted, they will be the ones who have the judgement an insight into their own child's development.