Engineers twice getting a low grade study again (6)
I believe the answer is:
reread
'study again' is the definition.
('read' can be a synonym for 'study' so perhaps 'reread' is OK for 'study again')
'engineers twice getting a low grade' is the wordplay.
'engineers' becomes 're' (abbreviation for Royal Engineers).
'twice' says to double the letters.
'getting' means one lot of letters go next to another.
'a low grade' becomes 'ad' (I am not sure about this - if you are sure you should believe this answer much more).
're' doubled is 'rere'.
'rere'+'ad'='REREAD'
Can you help me to learn more?
(Other definitions for reread that I've seen before include "Peruse or scan again; it's dearer" , "Give script second seeing to" , "Perused again" , "Study text again" , "look again at manifesto?" .)