Longhill High School in Rottingdean, close to Brighton, punished a number of boys earlier in the week for wearing shorts, which staff said were not an approved part of school uniform.
Head teacher Kate Williams told The Argus: "Students have access to water in order to keep themselves hydrated. We have made reasonable steps to ensure that classrooms are as comfortable as possible.
"I have high standards regarding uniform, and today, in the warm weather conditions, these high standards have been challenged by approximately two per cent of parents/students."
Michael's mother Angela Parker said: "We're fully in support of them. I think what the headmistress is doing is discrimination and I'm extremely proud of Michael and his fellow protesters. It's taken a heck of a lot for teenage boys to go to school wearing skirts."
Kodi's father Wesley told the Daily Mail he thought it was 'madness' for the school to punish boys for wearing shorts: "The shorts (Kodi) had on have the school logo on them and I think should be allowed to wear them on hot days. The school say they have to wear school uniform and the shorts are.
"The boys have done this to prove a point and I think it's brilliant. I don't think Kodi will wear the skirt all summer but I do think he likes the attention."
The boys were permitted to keep the skirts on on Thursday and Friday without punishment. Miss Williams said: "Students can choose to wear any part of the agreed school uniform."