More than 50% of schools in England closed or restricted attendance because of this week's teachers' strikes, according to government data.
Teachers belonging to the National Education Union (NEU) walked out on 15 and 16 March.
On 15 March, junior doctors, civil servants, London Underground train drivers and some BBC staff also took strike action.
It was one of the biggest days of action since the wave of unrest began.
Data released by the Department for Education showed 47% of all schools in England were open but restricting attendance, and 6% were fully closed on both strike days this week.
Secondary schools were worst affected, with 79% restricting attendance and 5% fully closed on 15 March. On 16 March, 80% restricted attendance and 6% were shut.