I am a teacher and I love when my students play this game, however I will not have them pay for a subscription, so if you could figure out a way to play for free for schools that would be great. Because this is an awesome learning tool, but you've made it cost money and that stinks.
I understand that this could create problems for schools and we might look at adding some special functionality for educational purposes in the future. We've also recently added group accounts which, while not free, reduces the price a great deal, perhaps that could be an alternative.
For more information regarding the latest changes please see: Regarding the latest changes to non-pro functionality