my 7yo son with diagnosis touches himself inappropriately

Hello all, my 7yo son who has a asd diagnosis touches and rubs himself in his private area over his clothes, now i know it is quite normal for kids to explore their bodies, but this is while he is watching tv, or even at school. I ask him to do it in is bedroom privately if he needs to, but he just shouts at me not to look. It is quite obvious what he is doing when he does it and he goes to a mainstream school so the conversations with his teacher are frustrating- as i feel the teacher doesn't understand autism- and hes just naughty/innapropriate. any help is welcome, is this common?