Vale of Glamorgan Council says Albert Primary School in Penarth has been closed due to damaged ceilings - and will probably have to remain closed for the remainder of the week.
It says staff noticed yesterday that there were areas of loose plaster on two ceilings.
After an inspection, it was decided the school should be closed for further investigations.
Parents have been told the primary school - which has 450 pupils - will probably have to stay closed this week, while repairs are undertaken.
Next week is half-term.
The council says there is no issue with asbestos in the ceilings.
– Cllr Chris Elmore, Cabinet Member for Children’s Services
Our officers think the damage has been the result of a water leak, probably caused by the extremely heavy rain we had over the weekend. The damaged ceilings are over two halls, which lead to the classrooms.
My priority is the safety of the children and staff, so unfortunately we have to close the school while we make the ceilings safe. We apologise to parents for the inconvenience and I will make sure our officers do everything they can to have the school open again as soon as possible.