M.A.
I have two 12 year old daughters. They do not share a room but they are upstairs away from us and across from each other. Their bedtime is 10:00pm and they tend to finally get lights out at 10:30-10:40. If we catch them later than 10:15pm with lights still on or talking, not in bed or whatever the case should be, then the next night they have to go to bed 30 minutes earlier. Each time they do it, 30 minutes earlier...they start to learn they don't like going to bed at 9-9:30pm.
Hope this helps.