Strange? I don't know if it's really all that strange for a kid that age, with or without AS to be curious. But I'm not so sure it's just that.
Doesn't belong in school though, and AS is no excuse for it. There are lines that should never be crossed regardless of disability.
It doesn't sound much like curiosity for him. Sounds like an obsession. He should NOT be exposing other kids to it in school, and just shouldn't be watching anywhere, much less there.
You want to wake him up a little? Do a search on the Internet. I remember a story recently about a bunch of high school kids who were sexting each other, and ended up being charged with distribution of child pornography. Exposing minors to pornography IS a chargeable offense in many places, even if you're a minor yourself. Don't know if it'll make an impression on him but it's worth a try.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...