Members of the SSTA teaching union are taking part in industrial action in a dispute over workloads.
The union welcomed moves by the Scottish government to reduce workloads but said it was unlikely to have an impact this session.
It argued that a “very large” number of its members had voted in favour of action short of a strike.
Education Secretary John Swinney said there was “no justification whatsoever” for the move which benefited no-one.
A total of 40.8% of SSTA (Scottish Secondary Teachers’ Association) members voted in the ballot and 91% voted in favour of taking industrial action.
Mr Swinney has urged SSTA members not to participate.
Earlier in the month he said: “I have taken swift action in response to feedback from teachers and others, to de-clutter the curriculum guidance and review the workload demands placed on teachers by local authorities.
“As these measures bed in, I ask teachers to continue to work with us to ensure that together we can create more time to teach our young people, and help contribute to closing the attainment gap.”
But the SSTA’s general secretary Seamus Searson said the union had “no option” but to take part in industrial action.