Instruction in reduced working (6)
I believe the answer is:
lesson
'instruction' is the definition.
(I know that lesson is a type of instruction)
'reduced working' is the wordplay.
'reduced' becomes 'less' (a reduced amount).
'working' becomes 'on' (on can mean working or activated).
'less'+'on'='LESSON'
'in' acts as a link.
(Other definitions for lesson that I've seen before include "Teaching period" , "Reading or exercise for a pupil" , "Spell of teaching" , "Sermon or lecture" , "School period" .)