My 4 dcs do not dirty clothes at the same rate.
DD1 is growing up and also her trousers can keep a few days, the tops smell of "adult" after one day, I would not dream of letting her wear the same top two days in a row.
Ds2 is playing outside constantly and needs at least a change a day
Ds3 plays outside but much quieter games and can wear the same cloth 3 days no problem.
Dd4 is a nightmare, she goes and change herself several times a day, destroying the beautiful piles of clothes in her drawer.
for school uniforms, they tend to be able to keep the same trousers a couple of days in a row but get clean top every morning.
""*by 'straight in the wash' I mean on the floor, in their beds, tucked behind cushions on the sofa rather than 'in the washing bin'""
Pretty much the same here with one little difference, they make the effort to go all the way to the "batroom cupbard" where the laundry basket is, they open it but then they find it to hard to actually put the clothes in the basket and just drop them on the floor, actually touching the basket but NEVER actually IN it!!! That drives me mad!