Group travelling by sea or coach (6)
I believe the answer is:
school
'coach' is the definition.
(both can mean to teach or train)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for school that I've seen before include "Educational institution" , "training centre" , "Educate; group" , "Train - a group of fish" , "company that's all at sea" .)