The strikes in England and Wales - the latest of seven days of action - have seen massive disruption across primary and secondary schools, with millions of pupils affected.
Thousands of teachers will walk out of schools on Wednesday in a bitter row over pay, affecting some seven million pupils. Planned strikes in Scotland have been cancelled.
Around 85% of schools will be either fully or partially closed by the strike action today, the general secretary of the National Education Union has said.
The strikes - the first of seven days worth in February and March - follow failed talks between Education Secretary Gillian Keegan and the general secretaries of teaching unions.