Crossword Genius

Head of school deficient, not working hard enough (8)

Ross

I believe the answer is:

slacking

'not working hard enough' is the definition.
(slacking means not doing enough work)

'head of school deficient' is the wordplay.
'head of' indicates taking the first letters.
'deficient' becomes 'lacking' (synonyms).
The initial letter of 'school' is 's'.
's'+'lacking'='SLACKING'

(Another definition for slacking that I've seen is " Slick nag (anag.)".)

I've seen this clue in The Times.
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