Book a certain school principal provided for dunce (8)
I believe the answer is:
bonehead
'for dunce' is the definition.
('bonehead' can be a synonym of 'dunce')
'book a certain school principal' is the wordplay.
'book' becomes 'b'.
'a certain' becomes 'one' (I've seen this before).
'school principal' becomes 'head' ('head' can be a synonym of 'school principal').
'b'+'one'+'head'='BONEHEAD'
'provided' acts as a link.
(Other definitions for bonehead that I've seen before include "stupid leader" , "Stupid person (colloq.)" , "dope" , "Stupid person with ossified cranium" , "Numbskull" .)