Second grade in a trial, ideally (2,4)
I believe the answer is:
at best
'ideally' is the definition.
(thesaurus)
'second grade in a trial' is the wordplay.
'second grade' becomes 'b' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'trial' becomes 'test' (synonyms).
'a'+'test'='atest'
'b' placed within 'atest' is 'AT BEST'.
Can you help me to learn more?
(Other definitions for at best that I've seen before include "In the optimal situation" , "Making every allowance" , "In the most favourable outcome" , "Assuming the most favourable conditions" , "In the most optimistic situation" .)