At DD's school the sixth formers wear school uniform for music concerts. Black trousers, white shirt, school tie. (They don't wear it everyday). They introduced a blazer this year, and a school skirt but year 11 up don't have these.
There was a suggestion the handful of sixthformers in the bands should buy blazers when the school took part in the local music festival last month, but strangely parents weren't keen!
DD's 18th birthday also approaching here.