There are many that don't. I recall a caving death around 02 or 03 where the instructor allowed a cavern diver to go along on a full cave class. The team turned, the student had an issue and he and the instructor had to stop to resolve it while the tag-a-long just kept going. As he was leading them out, he had no idea, got turned around, got lost and subsequently drowned. He wrote on his slate "I really F****** up". What a tragedy. He had no business being in that kind of situation just like a diver with less than a hundred dives has no business being alone in a class. Diving is about limits. Respect your limits or get hurt. Instructors need to respect the limits of their agency. You're not doing your student any favors by putting them in peril. None at all.Most instructional situations allow for "auditing" where you basically sit and watch someone else take a class.