Anger returned during school term (6)
I believe the answer is:
period
'term' is the definition.
(a term is a period of time)
'anger returned during school' is the wordplay.
'anger' becomes 'ire' (ire is intense rage).
'returned' is a reversal indicator.
'during' indicates putting letters inside.
'school' becomes 'pod' (I've seen this in other clues).
'ire' written backwards gives 'eri'.
'eri' put inside 'pod' is 'PERIOD'.
(Other definitions for period that I've seen before include "Span of time" , "Length of time, or a full stop" , "Duration or interval" , "Stop in America" , "Amount of time - US full stop" .)