I'm gathering views because I've started working doing music in a primary school and have reasonably free rein......
what would delight you if your child had achieved it at year 6? Being able to read music? Being able to use their instrument or voice to join in with others? Being able to play chords on a ukelele? a recorder? a tune on a violin? a tuba? Passing Grade x on an instrument? Singing or Playing a solo without looking mortified? Being in a rock band? Writing their own songs? Knowing and caring about their favourite musician? Having a positive can-do approach to lots of genres, including classical? Playing a rarer instrument like oboe? Knowing the secrets of rock improvision or blues improvision? Being able to say "I'm on grade 3"? Being able to say "I can play thistune on thatinstrument"?
go on, distract me from my other job (which is rather solitary and analytical) please.......