Mark King with a temperature in school (7)
I believe the answer is:
scratch
'mark' is the definition.
(I know that scratch is a type of mark)
'king with a temperature in school' is the wordplay.
'king' becomes 'CR' (short for Carolus Rex, King Charles in Latin).
'with' means one lot of letters go next to another.
'temperature' becomes 't' (abbreviation).
'in' is an insertion indicator.
'school' becomes 'sch' (abbreviation).
'cr'+'a'+'t'='crat'
'crat' placed inside 'sch' is 'SCRATCH'.
(Other definitions for scratch that I've seen before include "Withdraw from (competition)" , "Score with a sharp point" , "handle superficial irritation" , "Such a good golfer" , "minor injury" .)