Skipping English, Charlie possibly upset school (3)
I believe the answer is:
pod
'school' is the definition.
(term for a group of marine mammals)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for pod that I've seen before include "Seed case; whale herd" , "Natural container for pea" , "Long seed case" , "Hull" , "Pea shell" .)