Reading meta literature on the subject, I became convinced that the ability to address a group should be limited to moderators or admins. In this case, the parent that is elected representative for the class.
A collection of links on this topic, for my reference:
This frames the problem of group alerts, and the reasons why this idea could be horribly abused:
https://meta.discourse.org/t/can-include-a-group-of-participants-in-a-post-and-where-should-be-groups-management/7094?u=blau
This documents a feature that I see on meta.discourse.org but can’t reproduce on my setting:
There’s a 200 member limit in the UI, not in the application itself:
https://meta.discourse.org/t/group-seems-to-have-a-limit-of-201-members/11366?u=blau
A discussion of proposed feature:
https://meta.discourse.org/t/give-groups-full-names-and-allow-mentions/11168?u=blau