Like in 1.9 we have to enable "Override permissions for others" in teacher role... Thank you for correcting!
Humm... but that's a lot of new settings for teachers! (complaining for not having it and for having it!)
To close a forum the teacher will have to prevent students (correct me if i´m wrong):
> Delete own posts
> Reply to posts
> Start new discussions
As an admin, in order to only give permission to teachers to close forums, we must give them permission to override students permissions in other activities...
I wish closing a forum was easier, and not carry all these other permissions...
Thank you for your replies!