Head of kitchen prepared great dinner for school (12)
I believe the answer is:
kindergarten
'for school' is the definition.
(I've seen this before)
'head of kitchen prepared great dinner' is the wordplay.
'head of' says to take the initial letters.
'prepared' is an anagram indicator.
The first letter of 'kitchen' is 'k'.
'great'+'dinner'='greatdinner'
'greatdinner' anagrammed gives 'indergarten'.
'k'+'indergarten'='KINDERGARTEN'
(Other definitions for kindergarten that I've seen before include "Playgroup" , "Hamburger's first class" , "Pre-school institution for little children" , "Infant school" , "Where master may be" .)