Act for every class (7)
I believe the answer is:
perform
'act' is the definition.
(eg to perform or act on stage)
'every class' is the wordplay.
'every' becomes 'per' ('per' means 'for each' or 'for every').
'class' becomes 'form' (form class is a kind of class).
'per'+'form'='PERFORM'
'for' acts as a link.
(Other definitions for perform that I've seen before include "Carry out, accomplish" , "seen to make a profit?" , "Act or execute" , "function" , "Carry out (duties)" .)