Pass, even at school (3)
I believe the answer is:
col
'pass' is the definition.
(col is a term for a mountain pass)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for col that I've seen before include "A depression in mountain range" , "Mountain defile" , "Low area between peaks" , "Low point of a ridge" , "Officer" .)