Some 81 lycées, high schools for 15- to 18-year-olds, were shut on Thursday morning, according to the education ministry. About 17.5 per cent of primary schools were also affected by the strikes.
Workers were asked to halt production at oil refineries, and France was expected to import more electricity than it produced on Thursday because of disruption at nuclear plants.
Hundreds of thousands of people were expected to join strikes and street marches across France on Thursday as five unions staged a national day of action over the cost of living.
The five unions combined forces across the public and private sectors, demanding higher wages to combat rising prices and protected public services.
A coalition of unions urged workers, pensioners and young people to take part to intensify pressure on the government.
The government had sought to ease public anger over prices by releasing 10 million barrels of diesel from strategic reserves to bring down fuel costs.
Authorities anticipated 500,000 to 700,000 demonstrators, with tens of thousands more in Paris, in a mobilisation billed by one union leader as a great day of convergence.
In particular they sought a rise in the minimum wage, or Smic, currently €12.31 an hour.
More than 250 separate actions were planned for 5 November, with disruption already reported in schools, hospitals and public transport.
Ministers also promised school students to reform the unpopular Parcoursup university admissions platform and eventually replace it by 2028.