My sons recently became certified under NAUI. I was certified in 1987 and not much has changed. 7 week class meeting one day a week for 4 hours. You would study the work book before each nights class and then go over it for one to two hours depending then have water work after that. On the last night you take the exam. If you fail you get another chance. After passing exam open water dives are scheduled so you do 4 dives. My local dive shop will do custom or private certification schedule if you pay extra. Also since they have classes going at several different locations all at a different week in progress you can miss a night and easily make it up at one of the other locations.