Teachers across England are "solidly" supporting a 24-hour strike which has closed schools and disrupted lessons.
Members of the National Union of Teachers (NUT) walked out in a long-running dispute over school funding, pay and conditions and were joining rallies and marches.
The union said its members had shown strong support for the strike, which it added was being backed by many parents.
The NUT has written to Education Secretary Nicky Morgan calling for "meaningful" discussions to tackle issues it said were negatively affecting education.
The union claims funding to schools is being cut, leading to increased workloads for teachers and bigger class sizes - but Morgan has denied those claims and accused the union of organising a "political" strike.
Morgan also warned the strike would damage children's education, and that less than 10% of teachers had actively backed the walkout vote.