Explicit Videos on School Device

My son is able to watch YouTube at school and he has watched explicit rap music videos and who knows what else while at school. Our district has Chromebooks for all students which means they automatically have a Google account and YouTube account. It’s automatic, we (parents) do not have any say in this at all. I can’t even set parental controls on his school YouTube account. He brings his Chromebook home and can use YouTube whenever he wants.