In a first for the country, hundreds of pupils in southern France headed to school in uniforms on Monday as part of a national experiment to determine whether to make them compulsory, reports Radio France Internationale.
Uniforms have never been required in state schools in mainland France.
But President Emmanuel Macron last month announced a uniform trial at around 100 schools, with a view to making them mandatory nationwide in 2026 if it is successful.
Towns run by the rightwing make up the majority that signed up for the test, though some have met strong resistance from teachers, students and parents.
Critics say the money would be better spent in other areas of public education to improve learning.
The idea was first launched in January last year.
Around 700 students at four schools in the southern town of Beziers appeared to be the first to try it out in mainland France on Monday, after a school gave identical outfits a go in the overseas territory of La Réunion last month.