Male teachers and students in Spain have been coming to school in skirts in support of a boy who was expelled for wearing one last year.

The protest, which has seen the hashtag #ClothesHaveNoGender explode, is hoping to expose and challenge gender stereotypes.

It all kicked off when math teacher Jose Piñas wore a skirt in class after 15-year-old student Mikel Gómez was kicked out of school for wearing the same item.

His school then forced him to see a psychologist after he wore the skirt to promote gender nonconformity.

A video by Gómez describing the incident was watched by more than 2 million on TikTok.

Piñas too took to social media to deliver a message to his followers supporting the students.

He revealed he had suffered persecution and insults when he was younger.

"20 years ago I suffered persecution and insults for my sexual orientation in the institute where I am now a teacher," Piñas said.

"Many teachers, they looked the other way. I want to join the cause of the student, Mikel, who has been expelled and sent to the psychologist for going to class with a skirt."

Teachers Manuel Ortega, Borja Velúquez and Jose Piñas (left to right) sporting skirts in their classrooms. (Photo / Twitter)

Other teachers joined the movement and wore skirts every day to school during May.

Their decision came after one of their own students was bullied with homophobic slurs.

"A school that educates with respect, diversity, co-education and tolerance.

"Dress how you want! We join the campaign #ClothesHaveNoGender."

Students took to social media and their schools in support of Gómez and the teachers' efforts as hundreds of boys turned up to school wearing skirts.

Meanwhile, a group of alumni — male and female — from schools in Galicia gathered in skirts for the past six months to join the protest against gender identity discrimination, el Público reported earlier this month, establishing a nationwide movement toward tolerance.

A number of institutes have since offered a course on gender equality.

"They always tell us about the need to learn mathematics, history, language … But not about something as important as equality, and not only about gender," a protester said.