Make a mistake rotating students (4,2)
I believe the answer is:
slip up
'make a mistake' is the definition.
(slipping up is a kind of making a mistake)
'rotating students' is the wordplay.
'rotating' says the letters should be written in reverse.
'students' becomes 'pupils' ('pupil' can be a synonym of 'student').
'pupils' back-to-front is 'SLIP-UP'.
(Other definitions for slip up that I've seen before include "Make a mistake, on a banana skin ?" , "Informally, make a mistake - lose footing?" , "Mistake, blunder" , "err" , "Small error" .)