Footage of school students being forced to kneel with their hands behind their heads by French riot police has sparked outrage on social media.
A demonstration by students outside a school in Mantes-la-Jolie, west of Paris, ended in clashes with police and more than 140 arrests.
Students are angry at plans to reform the exam system, which they say will limit opportunity and breed inequality.
It comes as France prepares for further violence from "yellow vest" protesters.
Police said that those arrested at the Saint-Exupery school were suspected of taking part in an "armed gathering", adding that officers had wanted to break up a situation that was getting "out of control", Le Monde newspaper reported.
However, Paris Communist councillor Clémentine Autain said the images of students forced to kneel in dirt while facing brick walls were "frightening", "humiliating" and "unacceptable".
D'autres images de l'interpellation de dizaines de lycéens, aujourd'hui à Mantes-la-Jolie. pic.twitter.com/ghv8K91e7l— Violences Policières (@Obs_Violences) December 6, 2018
Frédérique Rolet, of France's education union the SNES-FSU, said she found the footage "unbearable", according to French radio station Europe 1.
The head of Oxfam France, Cécile Duflot, tweeted that she felt the scenes from the Mantes-la-Jolie school were "simply intolerable".
Ms Duflot also shared a report produced by former French high school students who participated in demonstrations dating back to the 1960s.
In it, they state that the actions taken by authorities in response to the recent protests have been "disproportionate".
"We blocked our high schools, occupied the streets," the report reads, adding: "None of us have ever been taken into custody... we were not gassed at close range in front of our schools."
Students across the country have been angered by President Emmanuel Macron's plans to change the end-of-school exam, which is known as the baccalaureate and is required for entrance to university, as well as the university admissions platform Parcoursup.
Student Louis Benzerrouk said on Thursday that he was demonstrating because young people "are not listened to".
"We are despised by [Macron and his government] ... we really have the impression that they are going in the opposite direction," he said.
Another student, Milena Arvois, said the planned reform will "kill the vocational schools", adding that she was also against an increase in fees for foreign students "because that will be a disaster".
Dozens of schools were blockaded in cities across France this week, including in Marseille, Nantes and Paris.
The "gilets jaunes" ("yellow vest") protesters, so-called because they take to the streets wearing the high-visibility yellow clothing required to be carried in every vehicle by French law, initially complained at a sharp increase in diesel taxes but the demonstrations have now widened to include other sources of discontent.
Mr Macron said his motivation for the increase was environmental, but protesters accused him of being out of touch.
The government later scrapped the plan but the yellow vest protesters have since issued more than 40 demands to government, including a minimum pension and widespread changes to the tax system.