School in Wales will be made to offer cheaper, gender-neutral uniform options from September, as the Welsh government seeks to tackle the rising costs of school clothing for families.

The statutory guidance issued by the Department for Education means Welsh state schools that are revising their uniform codes will need to avoid exclusive deals that force parents to buy from a single supplier, and must ensure that uniform items are widely available, avoiding expensive logos and designs.

The new rules also mean schools can no longer have separate uniform codes for boys and girls, so that trousers or shorts, for example, will be available for either to wear.

Kirsty Williams, the Welsh minister for education, said the costs of school uniforms were a long-running issue for families. She said the new code gave the government in Cardiff the chance to revise its guidance to give it a legal underpinning.

“It gave us an opportunity to look at the rather outdated way we look at uniforms, with lists of items for girls and lists for boys, which was a very old fashioned way of looking at how children should dress for school,” Williams said.

The new rules will also apply to PE and sports kit, which are often among the most expensive items that families need to buy. According to some estimates, school uniform can cost more than £300 per child at secondary school, with that cost rising if expensive blazers or hi-tech sports kit has to be included.

Parents in Wales will be able to lodge complaints if schools fail to meet the new rules, meaning that school leaders will have to demonstrate to the government that they have sought to follow the statutory guidance.

Williams said the cost of uniforms was really challenging for some families, with the Welsh government also extending its pupil development grants for children on free school meals to help with uniform costs at the start of each key stage.

“What we will expect school governors to consider are ways of keeping down the cost of uniform. That should include stipulating basic styles and colours, meaning that items can be bought from more than one outlet,” Williams said.

A study by the Children’s Society last year found that the high cost of uniforms was partly the result of schools requiring parents to buy clothing from specialist shops rather than at supermarkets or high-street chains.

An investigation by the Competition and Markets Authority found that sole supplier agreements may be in breach of competition law, and added about £10 to each item’s price.

Wales’s decision to use statutory guidance to enforce the new rules is in contrast with England, where the Department for Education has only voluntary guidelines. These state that “governing bodies should give highest priority to the consideration of cost and value for money for parents” in sourcing school uniforms.