Mr Miller said school leaders, the governing body and the county council had worked throughout the Christmas period to find a solution for all the children.
He said: “The structural engineer advised us in the last week of the term that further detailed surveys and investigations need to be undertaken across the whole site.
“The report from the engineer has been received and states that cracking and wall movement is now widespread and progressive and has accelerated over recent weeks and days.
“As such he can no longer confirm that the school building is safe to operate for students, staff and visitors.”
The headteacher said the school would use two teacher training days on 5 and 6 January to prepare the alternative locations for classes.