Handy error in school? (7)

I believe the answer is:

misdeal

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'handy error' is the definition.
'misdeal' can be an answer for 'error' (thesaurus). I am not certain of the 'handy' bit.

I can't explain the remainder of the clue.

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(Other definitions for misdeal that I've seen before include "Wrongly issue" , "Give out cards incorrectly" , "Faulty issue of cards" , "Right hand that isn't" , "Give out the cards wrongly" .)

I've seen this clue in the Evening Standard.

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