Around 90 NUT union members at two secondary schools in Haringey, north London, struck on Wednesday of last week.
It was the first day of sustained action over the victimisation of Julie Davies, Haringey NUT divisional secretary.
Fortismere and Highgate Wood schools were hit by the walkouts.
Workers are outraged that some secondary school heads refuse to sign the union access agreement unless Julie is sacked as union rep.
Workers were set to strike on Wednesday and Thursday this week followed by three days next week.
Strikers have received support from the public and parents. Both schools had parents evenings the night before the strike. Teachers found many parents were in full agreement with them.
Workers plan to lobby a full meeting of Haringey council on Monday 24 November from 6pm.
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