Start of lesson, they bring in students (8)
I believe the answer is:
learners
'students' is the definition.
(I've seen this before)
'start of lesson they bring in' is the wordplay.
'start of' indicates taking the first letters.
'they bring in' becomes 'earners' (people who earn or bring in money).
The first letter of 'lesson' is 'l'.
'l'+'earners'='LEARNERS'
(Other definitions for learners that I've seen before include "In cars, they must display L-plates" , "Pupils" , "Trainees" , "Students, apprentices" .)