Our school seems to follow what seems to be the standard formula: 3 months on average between lower ranked belts, 6 months to a year between brown and black, 2 years from 1st degree to 2nd, 3 years between 2nd and 3rd and so on... And of course all of those times are averages, exceptions have been made depending on students' abilities...

We have a school wide designated testing. 3rd Friday of every month, but similar to what Tori said, we're tested when sensei says we're ready, and we never ask. He explained when we signed up that we need to be able to perform our moves on command, and have X # of attendance which increases as the rank goes up. It's a fair system I think because who better to know if we're ready then the sensei?

At our school it routinely takes from 8 to 10 years to get to shodan -- though we do have one particularly talented teenager who made it in 7 1/2 years, after training intensely 5 to 6 days a week for at least the 2 years preceding it. We have testing every 3 months, but most people take at least 6 months to a year or longer to reach the next level, even if they know all of the requirements pretty well. Our teacher is very picky about every detail of our basics, even at the lower ranks, which can sometimes be pretty frustrating, but on the other hand, I think we have a really good school. We do really well in tournaments, but it's not like our teacher holds us back so we can compete against lower ranking students. In the only tournaments we go to, the divisions you compete in are based on the number of years training rather than rank in your school. I think it's beginner for less than a year of training, novice (colored belt) for less than 2 years, intermediate (brown belt) for 2-4 years, and after 4 years of training you compete in the black belt division. This means that we have many green belts competing against black belts. They don't usually win, but our black belts usually do!