At Marseille's Victor Hugo high school on Thursday, the teachers were inadvertently splashed as a student attempted to throw petrol into a rubbish bin, local authorities said.
Earlier the prosecutor's office had said the teachers had been assaulted and "doused in petrol".
At another school in the city, Saint-Exupery high school, hundreds of young people surrounded a fire truck that had arrived to put out a blaze in the morning, police said. The attackers forced the firefighters to flee the vehicle, then set it alight.
Another blaze hit a school in the western city of Nantes, fire crews said.
French education minister Edouard Geffray said on Thursday evening that he would successively meet representative staff unions, parent associations and student associations on Friday.
The demonstrations and blockades, which began last week, have become a political flashpoint at a sensitive moment for the government, which announced a series of deeply unpopular spending cuts in its 2027 budget on Thursday.
Prime Minister Sebastien Lecornu's office held a crisis meeting on Thursday afternoon on the protests, which have left dozens of people injured. Hundreds have also been arrested, most of them teenagers, officials have said.
Students have accused the police of using heavy-handed tactics, including the use of tear gas.
The government criticised the violence that broke out during some of the protests, but said difficulties in high schools should be acknowledged and addressed.
Interior minister Laurent Nunez said in some places troublemakers were moving from school to school to incite violence.
Geffray called for schools to hold classes remotely if protesters were blocking their premises.
"Violence will not keep our students from their fundamental right to an education," he said on X.
