Lister was hired to teach maths to teenagers, some of whom will be trans, quite inevitably. If Lister's strong personal objection to the existence of trans people means he can't professionally and appropriately address and interact with trans teenagers – who have every right to study maths – then Lister evidently cannot do the job he was hired to do.

Since he apparently wants to be an anti-trans campaigner, then he should quit his teaching job, anyway, and see which anti-trans groups are hiring.

In the meantime, the rest of the teachers at the school can just get back to teaching. Which, duh?