Teachers across Northern Ireland are taking part in a 12-hour strike.
The stoppage - on the same day thousands of health workers are also set to walk out - will run until midday on Tuesday in a dispute over pay and the future of the profession.
Members of each of the five main teachers' unions in NI are to take part and schools will reopen at noon to provide free school meals.
Ian McGonigle, NEU NI president, said pay for teachers has fallen by almost 40% in real terms since 2010.
"We are not only striking for ourselves, but for the future of the teaching profession and our colleagues too," he said.
"We all know teachers who are so burnt out they are going part-time in droves or on long-term sick absence, colleagues at the beginning of their careers whose take-home pay will be irreparably damaged and reduce their earning power across their entire career.
"For children without the SEN (special educational needs) support they need, or lost in the backlog waiting for assessment, for children whose education is at a detriment because of larger classroom sizes and less adults in the room, for the parents footing the bill because the school cannot afford basic supplies - we are taking this stand for them."
Gerry Murphy, Northern Secretary of the INTO union, said teachers hope to encourage employers and the Department of Education to the negotiating table.
"The decision to strike is one INTO members have not rushed into - indeed all of the recognised teacher trade unions have been very careful to manage this dispute in a way to minimise the disruption to the education of the children and young people in their care," he said.
"The harm being wrought across the education system due to systematic underfunding over the past decade is the real threat to the future of our children and young people.
"INTO members and their colleagues in the other recognised teacher unions have had enough.
"Enough of being forced to accept salaries that have not increased in real terms over the last 15 years, enough of increased workloads, enough of being forced to compensate for lack of resourcing and support for those in their care.
"Teachers are reasonable and sensible people and when they are moved to take strike action then the Government should listen.
"The five recognised teachers' unions are working together to achieve a decent and fair pay rise for all teachers and school leaders."
Some health workers will also strike on Tuesday over pay and conditions.
The Nipsa union said thousands of its members in the health service will take part in a 24-hour strike.
They include workers in domiciliary care, social work, ambulance workers, administration and nursing staff.
Padraig Mulholland, Nipsa deputy general secretary, said action by education and health workers is a "warning to employers that workers are not prepared to accept real-terms pay cuts and the destruction of services".
"We must have inflation-busting pay rises for all health service workers and an end to the chronic understaffing that puts lives at risk," he said.
"We cannot have a decent health service if thousands of posts are vacant and the staff are living in poverty.
"It is time for the whole trade union movement, public and private sector, to join together to fight to improve living standards and to defend services.
"Patient safety remains very important for health staff who will take industrial action. Discussions are ongoing to ensure the employers take the necessary steps to protect patients during the dispute."
A rally is set to take place at Belfast City Hall from around 10.15am after workers march from the Royal Victoria, City Hospital and the Mater.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know.