Joe Stratton rocked up wearing shorts on a roasting first day of term at de Stafford School in Caterham, Surrey.
To his shock, the 15-year-old was told that shorts were only permitted during the summer term, and he was faced with the choice of wearing either trousers or a skirt on September 5, his mum said.
On that day, the UK was flirting with a heatwave threshold, as Brits nationwide lapped up scorching temperatures of up to 30C.
The year 11 pupil chose the latter, wearing the skirt for the next two days.
Mum Jo told SurreyLive her son was willing to don the skirt “every day that he felt too hot to wear trousers”.
She went on: “He said most of his teachers either didn’t notice and didn’t say anything at all – well they must have noticed – or they were supportive of him.
“I don’t think they expected him to actually do it.”
Joe’s dad Ronnie hailed his son for being a “legend” throughout the ordeal.
“At first, he thought he was going to get ridiculed and have the mickey taken out of him,” he said.
“But, like I told him, at the end of the day, you stand up for what you believe in.
“Why should he go to school hot and uncomfortable and then try to function in school?
“To function and be uncomfortable and hot, I don’t think is right.”
Jo added: “Most of the teachers in his lessons were quite proud of him for finding a peaceful way to prove his point that didn’t hurt anybody and made a good point.”
Jo revealed that on the second day of Joe wearing a skirt she was told children would be able to wear shorts on September 8.
The school confirmed it had sent a letter written by the Head the day before to say pupils could wear summer uniform.
“The current intention is to revert to full normal uniform from Tuesday 12 September with temperatures dropping back,” Headteacher, Jeff Place said in a letter.
“We will carry out a more formal review of uniforms in due course, particularly regarding shorts as part of Uniform A for all times of year.”