Student employed in underwear factories (6)
I believe the answer is:
plants
'factories' is the definition.
(manufacturing plants)
'student employed in underwear' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'employed in' means one lot of letters goes inside another.
'underwear' becomes 'pants' (I've seen this before).
'l' inserted within 'pants' is 'PLANTS'.
(Other definitions for plants that I've seen before include "Sets seeds in the ground" , "climbers?" , "Vegetable organisms" , "Settles" , "Trees, shrubs etc." .)