At the Helene Boucher lycée, or high school, in Paris' 20th district, protesters laid rubbish bins and bicycles on their sides to create a makeshift barricade in front of the school.
Like hundreds of others around the country, the school was closed.
Authorities began shutting schools last week to take some steam out of the demonstrations after widespread damage to schools and mounting injuries among staff, students and police.
French media also reported protests in other cities and towns on Tuesday morning as labour unions called for workers to demonstrate later in the day in support of the high school movement that is rattling the government of President Emmanuel Macron.
The government's response has been muscular: police made more than 5000 arrests last week, 85 per cent of them minors.
But the police's widespread use of arrests, tear gas and riot-control weapons against teenage demonstrators is fuelling defiance and angering some parents and teachers.
At Helene Boucher, parents and other adults on Tuesday positioned themselves between protesters and police forces that kept watch.
School blockades and protests started in the Paris region in mid-September and spread to other cities and towns.
Demonstrators are expressing an array of grievances, often centred on complaints that resources and opportunities for advancement are sorely lacking for students in disadvantaged schools despite the promise of France's national motto: "Liberty, Equality, Fraternity".
Pupils have focused attention on run-down classrooms that lack basics such as desks and chairs, roast without air-conditioning in summer, and are even rat-infested.
Other widely shared complaints are that schools lack sufficient staff and that pupils' workloads are exhausting.
French high schoolers' compulsory school hours are among the highest in Europe.
