The limit is not in the application itself, it is in the way you deploy it.

On one end I have seen deployments with just a couple of BBB servers performing poorly and on the other end, deployments with over 3000 BBB servers working as a charm.

Lets say 150 users per server (assuming your servers can handle that) * 10 servers would give you 1500 users. It is normally more than enough for a small institution.

But for a K12 board, 150 users * 300 = 45000 total users concurrently sounds just about right.

I would personally not use this procedure for production, but I know that there are some institutions using it just as is. And some others with just minor tweaks.