One getting on train — and staying at school? (7)
I believe the answer is:
boarder
'one getting on' is the definition.
(eg someone boarding a train)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for boarder that I've seen before include "School liver-in" , "Schoolchild perhaps" , "Residential pupil" , "Lodger - invader of boat" , "Pupil who lives in school" .)