When lecturing, I leave something to help the pupils (3-4)
I believe the answer is:
eye-drop
'something to help the pupils' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'when lecturing i' is the wordplay.
I cannot really understand how this works, but
'i' could be 'eye' (I've seen this in other clues) and 'eye' is located in the answer.
The remaining letters 'drop' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'leave' is the link.
Can you help me to learn more?
(Other definitions for eye-drop that I've seen before include "A poetical tear?" , "A tear (Shakespeare)" .)