How to disable chat in Microsoft Teams meeting

Our school is having an issue with this feature. It only works if our users schedule a meeting outside the channel. As soon as we connect a channel to the meeting, the option "allow meeting chat" and to drop down to select "in meeting only" disappears. The entire row for allow meeting chat is missing. We need to use our channels for class invites but for our younger students, we do not want the chat to continue after the meeting has been closed. I worked with Microsoft Support today and they did not have any answers but to wait to see if enabling chat in policies works. Although, "not enabled" for participant meeting chats also did not take away the message chats. Anyone heard of this issue with channel meetings?