School enrollment size, what is possible?

I was reading about a TKD school about 30 miles from where I live that has 2000 students. Granted, this is probably the biggest martial arts school of any kind in the world, but it got me to thinking, how big are most BJJ academies, and how big are the biggest ones? I know Renzos is huge but seems to be an outlier, and is located in the largest metropolis in the country. Any input? Relative sizes of schools would be good to hear, and size of town the school is in.