About to be put back in school ground (7)
I believe the answer is:
terrain
'ground' is the definition.
(terrain is land or ground)
'about to be put back in school' is the wordplay.
'about to' becomes 're' (I can't justify this - if you can you should believe this answer much more).
'be put back' says the letters should be written in reverse.
'in' means one lot of letters goes inside another.
'school' becomes 'train' (school can mean to train or coach).
're' written backwards gives 'er'.
'er' put into 'train' is 'TERRAIN'.
Can you help me to learn more?
(Other definitions for terrain that I've seen before include "Stretch of land of a particular sort" , "Tract of land with prevailing characteristic" , "Land (as base for action)" , "Ground - rare tin (anag)" , "Physical features of a tract of land" .)