Private clans and subscription for pupils

I wanted to create a private clan so that I can track my pupils’ progress.
In order for my students to join, do they also need to have a subscription?

Yes, a subscription is required to join a private clan.

That is unfortunate. I will have a class of students starting next month. Most likely they won’t have a subscription at the beginning of the year. I guess I’ll just have to monitor who is in the clan and kick them out if they aren’t in my class.