Train from Switzerland passing through bogs on the climb (6)
I believe the answer is:
school
'train' is the definition.
(both can mean to teach or coach)
'switzerland passing through bogs on the climb' is the wordplay.
'switzerland' becomes 'ch' (short for Confoederatio Helvetica, its Latin name).
'passing through' indicates putting letters inside.
'bogs' becomes 'loos' (I've seen this in another clue).
'on the climb' is a reversal indicator (in a down clue, letters climb up).
'loos' back-to-front is 'sool'.
'ch' put within 'sool' is 'SCHOOL'.
'from' is the link.
(Other definitions for school that I've seen before include "Forms" , "Where 2 takes place" , "Centre of learning" , "Group of pupils, fish" , "training centre" .)