Video report by ITV News Consumer Editor Chris Choi
Despite a supermarket school uniform price war, many parents are having to make sacrifices in order to kit their children out for the new academic year.
ITV News has seen exclusive data that shows most state schools insist that at least some of the clothing for uniforms comes from particular outlets.
Figures from the Schoolwear Association show 75% of primary schools and 50% of secondary still have "sole supplier" arrangements.
Many believe these restrictions stifles consumer choice and limit fair competition.
Figures show these rules can add as much as £10 to a single item of uniform.
These "sole supplier" arrangements are also being criticised because they are stopping hard-pressed parents, such as mum Charlotte Hughes, being able to find affordable uniforms.
Ms Hughes told ITV News she had been forced to "make sacrifices" in order to afford the clothing on her daughter's schools official list.
A separate ITV News survey showed the demand for second hand uniforms has hugely increased, with a 164% annual rise in demand at uniform banks.
One dad told ITV News how he had fought his school's sole trader uniform policy and won.
"It (the uniform) added up to about £220.
"Clearly I'd seen cheaper uniforms in the supermarkets where you can buy a pair of trousers for £6/£7," Tim Crossland said.
But the trade defended the restrictions on where parents can buy their child's uniform.
Matthew Easter from the Schoolwear Association told ITV News that 80% of school uniforms were bought on the high street.
He said: "The garments we make are made out of robust fabric, constructed in a strong and robust way. And they're designed to last."
Headteachers say they will respond to concerns from parents as the new school year begins amid increasing economic hardship.