Improve workers in education (5)
I believe the answer is:
emend
'improve' is the definition.
(emending is a kind of improving)
'workers in education' is the wordplay.
'workers' becomes 'men' (man is a kind of worker).
'in' indicates putting letters inside.
'education' becomes 'ed' (abbreviation - e.g. sex ed).
'men' inserted inside 'ed' is 'EMEND'.
(Other definitions for emend that I've seen before include "Alter to improve (text)" , "Edit, improve" , "Make changes to (a text)" , "Correct and improve the text" , "Polish" .)