Scores of young people were pictured on their knees, with their hands on their heads for several hours during protests in December 2018.
ADVERTISEMENTA French judge will investigate allegations of police torture during student protests near Paris in December 2018.
Social media videos had sparked outrage across France, showing young people in handcuffs during clashes over high school disputes in Mantes-la-Jolie, west of the French capital.
Students, aged between 12 and 21, were pictured on their knees, heads down and with their hands on their heads for several hours, watched by armed police.
A police officer filming the scene could be heard saying: "This is a class that is wise."
French interior minister, Christoph Castaner, later reported that 151 people had been arrested, some carrying weapons.
No students were said to be injured, and a large number of those arrested were quickly released from police custody with a caution.
The police operation in Mantes-la-Jolie was part of a crackdown on days of protests over the French government's education reforms to Baccalauréat examinations, which determine a student's eligibility for university.
After the incident, several families and the high school student union UNL lodged appeals against "police violence" but a preliminary internal investigation by the police was dismissed in July 2019.
The head of Oxfam France, Cécile Duflot, tweeted that she felt the scenes in Mantes-la-Jolie school were "simply intolerable".
The mayor of Mantes-la-Jolie, Raphael Cognet, also released a statement after the images circulated on social media, "condemn[ing] with the biggest firmness this violence and ... the traumatism that people have gone through".
The new appointment of an investigating judge was requested in March by the Nanterre public prosecutor's office, a lawyer for the first complainant told AFP.
Complainants have accused the police of "torture by persons responsible for a public authority", six months after the first claim was registered by one of those arrested, according to AFP citing sources.
The investigation will also examine claims of the “torture of a 15-year-old minor, arbitrary violation of liberty by a person holding public authority, aggravated violence” and “dissemination without his consent of an identifiable person handcuffed and criminally challenged”.
But the Union of Police officers said "the country is walking on its head" after news of the judicial investigation.
"The intervention of police officers had put an end to the riots during which certain 'high school students' had set rubbish bins on fire and then thrown gas bottles inside," the union wrote on Twitter.