Teachers at three Stoke-on-Trent schools are on strike for a second time in a week in a dispute over pay.
Pupils were told to stay away from Trentham High, Holden Lane High and St Peter's High on Thursday.
The strikes started three months ago and more industrial action is planned for November.
They relate to a dispute over performance-related pay. Brian Cookson, NASUWT national executive member for Staffordshire and Stoke-on-Trent, said: " the schools have seriously breached the national agreement on pay progression and until they acknowledge that breach, we cannot move forward."
Four days of action have taken place since July at Trentham High and Holden Lane High, while at St Peter's three strikes have been held.