Can a teacher lock you out of class?

Well if you paid for them, then it should be addressed. Your money is being wasted. However, if you mean in COLLEGE, well professors have their own rules and if you're late, too bad. You have to adhere to their wishes because they ARE your boss. In the future your boss in the workforce won't care if your life's salary depends on it, he WILL lock you out if you are late and he is strict.