School prize went to son, finally (4)
I believe the answer is:
eton
'school' is the definition.
(famous UK public school)
'prize went to son finally' is the wordplay.
'finally' indicates one should take the final letters.
The final letters of 'prize went to son' are 'ETON'.
(Other definitions for eton that I've seen before include "Leading English public school" , "Public school near Windsor" , "Town on the Thames noted for its school" , "Note sent up to English public school" , "Town opposite Windsor on the Thames" .)