Faith in mediocre education (5)
I believe the answer is:
creed
'faith' is the definition.
(I've seen this before)
'in mediocre education' is the wordplay.
'in' indicates a hidden word.
'CREED' is hidden within 'mediocre education'.
(Other definitions for creed that I've seen before include "teleprinter" , "Catechism" , "Articles of faith" , "System of religious belief" , "Set of beliefs or principles" .)