Three years ago Maesteg Comprehensive School held its first "prom" party for its year 11 students to celebrate finishing their GCSEs.
Head teacher Helen Jones thought the new tradition imported from America was "fantastic" - but it also created a problem when they realised a pupil was not going to attend because of the cost of the outfit.
"It becomes an overwhelming experience for a lot of our children, particularly girls, with the pressure to look their very best," she said.
"It can run into hundreds [of pounds], if not thousands, and that's something that I never wanted to encourage."
So two of the school's PE teachers, Emily Scudamore and Annemarie Scarr, put out an appeal on social media for donations of prom gowns for pupils to use for free.
They have now received about 200 gowns, plus shoes and accessories, from ex-pupils, local people and businesses, including 30 brand new dresses from a wedding shop in nearby Pyle.
"It's hit a chord with a lot of people... the kindness of strangers and obviously through social media. I'm truly overwhelmed by the response we've had," said Mrs Scarr.
The school is holding a "pop-up" shop this week, and promoting a "vintage vibe" in case there is any stigma around borrowing the dresses.
Most of the gowns have only been worn once.
"It's not just about targeting those who couldn't afford the best dress. It's a real opportunity... to discourage them from this throwaway society that we live in, and also to instil a sense of community," said Mrs Scarr.
Sixth-formers Katelin Jenkins and Megan Curling, both 18, previously went to their own prom and are enthusiastic about helping with the pop-up shop.
"Some of my friends were spending huge amounts of money... It's because it's prom and everybody thinks 'I have to go big, I have to have that big dress' when you don't," said Megan.
Katelin agreed the prom event had come with "massive pressure".
"Don't worry about the pressure of 'Will I look right? How much has everyone else paid?' Just enjoy the night," she said.
The school is not stopping at dresses - it has also asked Bridgend College to help with hair and make-up and hopes to source suits for pupils in future.
Nearly a quarter of its pupils, above the Welsh average, are entitled to free school meals and Ms Jones had questioned whether they should be running the prom at all. But overall the pupils wanted to have the event, so the school has decided to do what they can to keep it "inclusive".
"Austerity has affected everybody and tends to hit areas like Maesteg and lots of Valleys communities first. Certainly the recent news of the closing of the Ford factory [in Bridgend] has ricocheted around the community. It's bound to impact on our families," she said.
"We also provide buses to the venue because we don't want the nonsense that comes with limos, you name it.
"There are enough pressures and trials for our young people at the moment to survive, without the added pressure of this, which is supposed to be a celebration of what they've achieved at the end of their formal education."