Four years.
Since you mention it, I've run my classes on a few principles:
- People must read up the assigned reading list before coming to class; no spoon-feeding, not for post-grads;
- During class, people will be given opportunities to display what they know; what they don't know is a matter that comes out during tiny little quizzes held every now and then;
- Dissent is encourage, but it has to be reasoned and argued dissent, not just publicity seeking to impress the girls;
- Dumb insolence will be punished but in a passive manner; you get less and less attention;
- Exam questions seek short answers to the point; rambling is discouraged;
- Every question is answered by me, and set aside in confidence, before the exam, and answers are benchmarked against those 'ideal' answers (not infrequently, students' answers have been better than mine);
- Every retort is encouraged, in the hope that it will turn out to be the point at which intelligent questioning of the unquestionable will start, but there is always the shambling Neanderthal who confuses bad manners with smart behaviour, and have to be executed swiftly and cleanly, but not in such a manner as to cause permanent harm.
Having read this lot, the unhappy thought occurs that this is more or less how I behave on PDF, except when I am bored and out of sorts and inclined to mischief.