Is this something new?
We got a letter from ds's school to say yr11s will have assertive mentors. Most of them will have their form teacher as their mentor under certain criteria some children will be given different mentors. DS seems to have been given a mentor that is not his form teacher, which I am pleased about as his current form teacher is not very good. They will meet with their mentors once a month.
I assume that by saying assertive they mean the mentor takes an active role setting up meetings, rather than the child only going to see their mentor when they think they need help.