Spur teacher to accept first of trainees (4)
I believe the answer is:
stir
'spur' is the definition.
(thesaurus)
'teacher to accept first of trainees' is the wordplay.
'teacher' becomes 'sir' (I've seen this before).
'to accept' indicates putting letters inside.
'first of' says to take the initial letters.
The first letter of 'trainees' is 't'.
'sir' going around 't' is 'STIR'.
(Other definitions for stir that I've seen before include "Thrill" , "Agitation - prison" , "Ladies' underwear" , "Prison - mix" , "Uproar" .)