Disobedient class's unacceptable behaviour (3,4)

I believe the answer is:

bad form

'unacceptable behaviour' is the definition.
(I've seen this before)

'disobedient class's' is the wordplay.
'disobedient' becomes 'bad' (associated in meaning).
'class' becomes 'form' (synonyms).
'bad'+'form'='BAD FORM'

(Other definitions for bad form that I've seen before include "Offence against convention" , "Reprehensible conduct" , "unruly class" , "Offending against conventions" , "Unacceptable behaviour" .)

I've seen this clue in the Sydney Morning Herald.

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