The school in south Wales was shut last week following the discovery of asbestos.
The first pupils are set to return to the newest part of the school this Friday but older buildings will remain closed.
Caerphilly County Borough Council said: “The council took the difficult decision to close the school in light of the findings of a structural report and we are not prepared to fully re-open the site until further investigations have taken place to determine the extent of the problem and the work needed to address the situation.”
Education Minister Leighton Andrews said all schools across Wales must report on asbestos levels by next week.