This school once was sanctioned (8)
I believe the answer is:
approved
I believe this is a double definition.
'this school once' is the first definition.
(approved school was a historical type of school)
'sanctioned' is the second definition.
('approve' can be a synonym of 'sanction')
'was' is the link.
(Other definitions for approved that I've seen before include "Officially sanctioned" , "Official" , "Given the OK" , "Okayed" , "OK'd" .)