Cane joker in school (6)
I believe the answer is:
switch
'cane' is the definition.
(I've seen this before)
'joker in school' is the wordplay.
'joker' becomes 'wit' (I've seen this before).
'in' indicates putting letters inside.
'school' becomes 'sch'.
'wit' going into 'sch' is 'SWITCH'.
(Other definitions for switch that I've seen before include "On/off device" , "Change over - whip" , "Change; hair-piece" , "Sudden quick change" , "Get change" .)