A failure as a schoolteacher? (5)

I believe the answer is:

amiss

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'as a schoolteacher?' is the definition.
I can't judge whether this definition defines the answer.

'a failure' is the wordplay.
'failure' becomes 'miss' (miss is a kind of failure).
'a'+'miss'='AMISS'

Can you help me to learn more?

(Other definitions for amiss that I've seen before include "error" , "Mistakenly" , "Badly - wrong" , "Not quite right" , "Haywire" .)

I've seen this clue in the Evening Standard.

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