This one has baffled me. Just read on another forum that it's chavvy to have DC not change out of school uniform once home.
I'm sure me and my siblings only wore our own clothes at weekends and on school holidays/non-uniform days. If it was a schoolday then we'd wear the same uniform set all week as well (but DM wasn't known for having the best hygiene standards, and we were only bathed once a week etc...this was in the 90s).