Sculpture shows upper-class in mess (6)
I believe the answer is:
statue
'sculpture' is the definition.
(I know that statue is a type of sculpture)
'upper-class in mess' is the wordplay.
'upper-class' becomes 'u' (similar in meaning).
'in' means one lot of letters goes inside another.
'mess' becomes 'state' (I can't justify this - if you can you should give a lot more credence to this answer).
'u' placed into 'state' is 'STATUE'.
'shows' acts as a link.
Can you help me to learn more?
(Other definitions for statue that I've seen before include "Carved likeness" , "Still work" , "Carved representation" , "Sculpture of person or animal" , "Model figure" .)