In short break class turns over a new leaf (7)
I believe the answer is:
reforms
'turns over a new leaf' is the definition.
(I've seen this in another clue)
'in short break class' is the wordplay.
'in' indicates putting letters inside.
'short break' becomes 'res' (I can't explain this - if you can you should give a lot more credence to this answer).
'class' becomes 'form' (synonyms).
'res' going around 'form' is 'REFORMS'.
Can you help me to learn more?
(Other definitions for reforms that I've seen before include "Changes for improvement" , "Makes changes" , "Mends ways, abandons badness" , "Adjustments" .)