A school group from small estate (6)
I believe the answer is:
assets
'estate' is the definition.
(I've seen this in another clue)
'a school group from small' is the wordplay.
'school' becomes 'S'.
'group' becomes 'set' (both can mean a collection).
'from' says to put letters next to each other.
'small' becomes 's' (abbreviation - e.g. clothes size).
'a'+'s'+'set'+'s'='ASSETS'
(Other definitions for assets that I've seen before include "Useful or valuable things" , "Useful skills" , "Possessions of material value" , "Valuable resources" , "Property owned by person or business" .)