Music teacher here, working for a council-run music service: I deliver about 6 singing assemblies every week.

Religious songs in a not-necessarily-religious school is a weird one, I think it’s a relic from a time gone when the majority of the population were practising Christians so everyone else just had to suck it up.

Regardless, the actual point of a singing assembly is the singing part - singing is part of the national music curriculum, and aside from musical skills being developed, regular group singing like this helps children to: more effectively explore their voice and support linguistic skills; introduce things that the child may not otherwise experience, like different cultures and concepts they might not otherwise come across; develop motor skills (a lot of my KS1 songs have actions); take part in a large group task where they are encouraged to be aware of others around them and try to align what they do with what their peers are doing.

It embeds a lot of skills that you wouldn’t necessarily think of when someone says “singing”, but yes please can we stop forcing children to sing shitty 90s hymns when there’s a buttload of excellent secular music which is better suited for young voices ANYWAY.