Thousands of children are missing lessons as teachers in Nottingham stage a walkout over proposed changes to school term dates.
Nottingham City Council are planning to introduce a five-term academic year with a shorter summer break in order to boost attainment. But members of the National Union of Teachers (NUT) have downed tools in protest at the plans which they say will be disruptive to pupils.
Assistant secretary of Nottingham's NUT John Illingworth said the union did not take the action "lightly".
"The council hasn't backed down on this issue so we have to get the message across because this move will have a negative impact on children."
The council has argued the new system, which would include fortnight breaks in May and October would help pace pupils' education and ease childcare issues during the summer.
Members of other teaching unions such as the NASUWAT and Association of Teachers and Leaders are not striking.
The council released a statement saying the "bold step" was proposed to ensure the school year structure supports pupils' learning and boosts chances of achieving their full potential.
"Many children simply fall out of the habit of learning over the long summer break so by shortening it to just over four weeks, there is a greater chance that pupils will remember their lessons and return to school in the autumn ready to learn."
The council added it hoped the move would improve attendance.