@wizz Hello! I have two boys that are 17 and 21 respectively. I might be able to help with the coding.
When you're ready to talk to him, just let him know that is totally okay to be curious about bodies and how different people have different bodies, but that its really important that when he's drawing bodies that he makes sure its okay with everyone. So like, its totally fine to draw in his own notebook or paper, but that its not okay to draw on things that don't belong to him, like math books that belong to the school. He wouldn't want someone coming into his room and drawing on his things without him saying its okay, so he needs to be respectful of others' property too. And that same concept goes for bodies, too. If he wants to draw bodies, he needs to make sure that its in a time and place that's okay with everyone. During school is not a good time for that sort of drawing because he's doing it in a public, shared space and everyone may not be okay with it. Its like if the class gets to have a special snack and everyone wants Butterfingers, but one of the kids is allergic to peanuts. Its not fair to him to be left out because of his allergy, so its better if everyone finds a different snack to have. Its okay to draw, but what he draws needs to be okay with the people he's around because a public space means anyone can see it and not everyone would be okay with it.