Parents have been left in limbo over school walkouts as strike secrecy leaves headteachers unable to plan.
The government has urged the National Education Union (NEU) to keep headteachers informed of which teachers plan to strike so that schools can plan lessons for Wednesday.
Advice on the union's website stresses that teachers do not have to tell schools if they plan to strike, The Times reports.
Thousands of schools are expected to be affected by tomorrow's strikes as teachers walk out, demanding higher pay.
