The teachers' strike on Tuesday will close at least 45 more second-level schools than originally feared.
The spread of the disruption could bring to about 400 the number of schools that will not open, forcing up to 200,000 pupils to stay at home.
It was known that up to half of post-primary schools would be closed because of a one-day strike by the Teachers' Union of Ireland (TUI) over pay inequality. These are schools in the education and training boards (ETB) sector, and the overwhelming majority of community and comprehensive schools, where the TUI is the sole or dominant union.
The Joint Managerial Body (JMB), representing the voluntary secondary sector - generally schools traditionally run by the religious as well as the growing number under the patronage of Educate Together - said it was aware of 45 of its 380 schools closing. The final figure may be even higher than this.
Meanwhile, up to 1,300 crèche owners are set to march with staff and parents in a national protest rally over the "worsening childcare crisis" next Wednesday, which will disrupt childcare services nationwide.
However, a threatened strike by up to 500 home helps in Dublin and Wicklow planned for Friday has been deferred. They say they will mount pickets on February 21 if the HSE does not transfer money to staff as part of a pay restoration agreement.