Beat schoolmaster, getting time inside (4)
I believe the answer is:
stir
'beat' is the definition.
(thesaurus)
'schoolmaster getting time inside' is the wordplay.
'schoolmaster' becomes 'sir'.
'getting time' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'inside' indicates putting letters inside.
'sir' enclosing 't' is 'STIR'.
Can you help me to learn more?
(Other definitions for stir that I've seen before include "Prison - mix" , "Agitate - disturbance" , "Commotion - prison" , "can > go forth" , "riot" .)