To have a word with my DS's teacher...

[Gert]

...for telling him he looks like an idiot (practising for school assembly which includes a dance - he has zero co-ordination!). He tries hard at school and behaves really well, generally.

2 HOUR rehearsal for an assembly?
WTAF?
Is it at the Albert Hall......for Her Majesty The Queen?

Initially I'd have been LIVID, but unless the teacher is known for being a bit nasty I'd have calmed down, had a think about what is more likely to have actually happened and gone with the 'messing around and being told if they didn't pay attention now they'd look like idiots at the performance'. Still not a wise choice of words in this day & age, but didn't do us any harm! If I had 30+ of them all day (especially with school performance pressure) & 'idiot' was the worst word I'd used, then I'd consider it a good day, a really good day, frankly 😬

No, that's standard for an assembly in addition to any work you've done in class.
Class assemblies are often a nightmare, many schools have scrapped the performance.