John gets left in school (5)
I believe the answer is:
elton
'john' is the definition.
(musician Elton John)
'left in school' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'school' becomes 'eton' (famous UK public school).
'l' placed inside 'eton' is 'ELTON'.
'gets' is the link.
(Other definitions for elton that I've seen before include ". . . . . John (musician)" , "Ben --; -- John" , "Sir - - John, singer songwriter" , "Let on he's John, the singer" , "First name of singer/songwriter born Reginald Dwight in 1947" .)