It's not a hate crime. A hate crime is an aggravating factor in an actual crime.
Thank you, Datun! When Mermaids throw this shit around, it's so annoying.
There is no such thing in the UK as a standalone "hate crime" in and of itself. If you commit a crime and your motivation is hatred of a protected group, then that's an aggravating factor and the crime can be classified as a) the actual crime and b) the actual crime + hate.
You can't commit a hate crime if there is no crime to attach it to.
If you assault a bloke because he snogged your girlfriend - not hate crime.
If you assault a bloke who is black because you are racist - hate crime.
Under no circumstances should a teacher openly ridicule a child for any characteristic, whether it's gender or something else. Under no circumstances should a teacher bully a child, whether it's about gender or anything else.
As to pronoun use in schools - case by case basis, with the child, teachers and parents coming to a mutual and negotiated agreement. Schools shouldn't be validating a trans identity in a pupil without the knowledge of parents, for example.