Be entitled to answer following two poor grades (7)
I believe the answer is:
deserve
'be entitled to' is the definition.
(I've seen this before)
'answer following two poor grades' is the wordplay.
'answer' becomes 'serve' (I've seen this before).
'following' means one lot of letters go next to another.
'two poor grades' becomes 'de'.
'serve' after 'de' is 'DESERVE'.
(Other definitions for deserve that I've seen before include "Justify" , "Severed (anag)" , "Warrant" , "Be entitled to" , "Merit (something)" .)