A pupil, too backward, should not be taken (4)
I believe the answer is:
loot
'should not be taken' is the definition.
I can't judge whether this definition defines the answer.
'a pupil too backward' is the wordplay.
'a pupil' becomes 'l' ().
'backward' is a reversal indicator.
'too' back-to-front is 'oot'.
'l'+'oot'='LOOT'
Can you help me to learn more?
(Other definitions for loot that I've seen before include "Tool for plundering" , "familiar officer" , "Steal (goods); money" , "Stolen property" , "Swag, booty" .)