You write: "I'm fully aware that it's the approach I'm taking with them, and not a problem of theirs"
Don't be too hard on yourself. The reason I am giving you no advice is that one of the reasons I stopped teaching in 11-16 schools in the UK to return to TEFL was that, after 32 years in the classroom, I still had problems with some children in that age range. I regret to inform you that even if you receive some helpful advice from other teachers, it may not work for you.
13/14 year-olds can be ... (I shall not complete that, because some moderator would only have to delete the expressions I would use.)