More than 100 schools in England are scrambling to make arrangements after being told to shut buildings with a type of concrete prone to collapse.
The government gave the order just days before the start of the autumn term.
Some pupils have already been told they will be learning remotely, in temporary classrooms or at different schools.
The government has not said when a list of affected schools will be published, drawing criticism from the Labour Party.
Shadow education secretary Bridget Phillipson, who said Labour had not seen the full list, urged ministers to "come clean with parents and set out the full scale of the challenge that we're facing".
On Thursday, Education Secretary Gillian Keegan said affected schools would contact parents directly, adding: "If you don't hear, don't worry".
Schools found with buildings containing reinforced autoclaved aerated concrete (RAAC) have been told they must introduce safety measures, which could include propping up ceilings.
A "minority" will need to "either fully or partially relocate" to alternative accommodation while those measures are installed, the Department for Education (DfE) has said.
