Urge school principals to become intellectuals (8)
I believe the answer is:
eggheads
'intellectuals' is the definition.
(egghead is a kind of intellectual)
'urge school principals' is the wordplay.
'urge' becomes 'egg' (I've seen this before).
'school principals' becomes 'heads' ('head' can be a synonym of 'school principal').
'egg'+'heads'='EGGHEADS'
'to become' acts as a link.
(Other definitions for eggheads that I've seen before include "academic talents" , "Slang intellectuals with lofty domes" , "TV quiz show" , "Slangy intellectuals with lofty domes" , "Boffins" .)