Nudge teacher's bottom in school (4)
I believe the answer is:
prod
'nudge' is the definition.
('prod' can be a synonym of 'nudge')
'teacher's bottom in school' is the wordplay.
'bottom' indicates one should take the final letters.
'in' indicates putting letters inside.
'school' becomes 'pod' (I've seen this before**).
The last letter of 'teacher' is 'r'.
'r' going into 'pod' is 'PROD'.
(Other definitions for prod that I've seen before include "Drop (anag.)" , "Poke - remind" , "Incite to action (with a stick?)" , "Poke with a stick" , "Poke with forefinger, stimulate" .)