School is not able to be inadequate (5)
I believe the answer is:
scant
'inadequate' is the definition.
(I've seen this in another clue)
'school is not able to' is the wordplay.
'school' becomes 'S'.
'is not able to' becomes 'cant' (cannot).
's'+'cant'='SCANT'
'be' is the link.
(Other definitions for scant that I've seen before include "Meagre" , "Scarcely sufficient" , "Insufficient, limited" , "Deficient, sparing" , "Little" .)