A white child of the upper classes is left behind (7)
I believe the answer is:
chablis
'a white' is the definition.
(I know that Chablis is a type of white)
'child of the upper classes is left behind' is the wordplay.
I cannot really understand how this works, but
'child' could be 'ch' (abbreviation for child) and 'ch' is present in the answer.
'is' is found in the answer.
'left' could be 'l' (common abbreviation) and 'l' is present in the answer.
The remaining letters 'ab' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for chablis that I've seen before include "Classic white wine from Burgundy" , "Burgundy town and white wine" , "French dry white wine" , "Town in north central France noted for white Burgundy wines" , "Dry Burgundy wine" .)