State schools are shut in Denmark for a second day because of a dispute between teachers and local authorities over working conditions.
About 90,000 teachers were locked out after negotiations broke down and nearly 900,000 pupils have no classes.
A teachers' union spokesman called the action "historic" for Denmark.
Gordon Madsen told BBC News that the government and teachers' employers wanted teachers to spend more time in the classroom during the school day.
The changes would mean younger children spending about two more hours in school daily and the oldest children three more hours, he said.
Mr Madsen said the teachers' time for preparing lessons would be reduced under the reforms. The teachers are pushing for a cap of 25 hours a week spent teaching, so that it is clear what counts as overtime.
The dispute affects children between the ages of six and 16. They are now spending their time at home with family members, or at their parents' workplaces or at youth clubs.
"Teachers are protesting in the streets all over Denmark," Mr Madsen said.
He accused the centre-left government of doing a deal on school reform with the local authority organisation KL, which pre-empted negotiations with the national teachers' union.
"It's the first time all the teachers have been locked out. It's a threat to the Danish model," he said, explaining that traditionally in Scandinavia workplace conditions are negotiated directly between unions and the employers without government interference.
Prime Minister Helle Thorning-Schmidt defended the plan to introduce longer hours in school, and said her government was not yet prepared to intervene in the dispute.
"We cannot accept that an average of three or four children in each class never learn to write at a level that enables them to go on to further education," she said on Tuesday.