Schools in England will be required to make sure second hand uniforms are available to help keep costs down for parents each year.
The Department for Education (DfE) will publish statutory guidance for schools today which will instruct them to ensure their uniform is affordable.
Schools are expected to have taken steps to adhere to the guidance before parents buy uniform for the academic year beginning in September 2022.
The Education (Guidance About Costs of School Uniform) Bill, which makes guidance given to schools about the cost of uniform policies legally binding, was passed in April this year.
It was first introduced by Labour MP Mike Amesbury and it received cross-party support.
Under the guidance, which is being published for the first time, schools will have to make sure second-hand uniforms are available.
Schools will also be advised to keep branded uniform items to a minimum and they will be encouraged to allow more high-street options.
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Education Secretary Nadhim Zahawi said: "School uniform provides a sense of identity and community for children and young people, and should be a real source of pride. But it must never be a burden for parents or a barrier to pupils accessing education.
"This new binding guidance will help to make uniforms far more affordable for families by driving costs down as we work hard to level up the country."
The guidance will require schools to use competitive and transparent contracts with suppliers, and it will say schools should make sure their uniform policy is published clearly on their website.
Mark Russell, chief executive of The Children's Society, said: "For too many years the cost of school uniform has been a heavy financial burden on many families, causing money worries and even debt, so these new guidelines to make sure school uniforms are affordable are extremely welcome.
"Until now, too many parents have had to fork out for expensive branded items rather than cheaper alternatives, while having to cut back on essentials like food or heating.
"So, we hope schools are able to start working with the guidance, which should ultimately make it much easier for families to kit out their children for school without breaking the bank."
Matt Easter, co-chair of the Schoolwear Association, said: "We welcome this guidance as it takes a balanced and proportionate approach towards ensuring parents get good value for money from uniforms, without creating unreasonable burdens on schools or uniform suppliers.
"Importantly, it reinforces that the majority of schools are already doing the right thing and, in most cases, will already be fully, or almost, compliant."
James Bowen, director of policy for school leaders' union NAHT, said: "It's important to remember that a large number of schools already work extremely hard to ensure that their uniform is affordable for families.
"Many schools also run schemes to provide support for families who might be struggling with the cost of uniform.
"That being said, we fully support the move to ensure that uniform remains as affordable as possible in every school.
"We know that an increasing number of families have come under financial pressure due to the pandemic, so measures that could reduce the cost of uniform are certainly welcome."