Problem for schools is forgiven, oddly? Hard to stop it (11)

I believe the answer is:

overfishing

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'problem for schools' is the definition.
I can't judge whether this defines the answer.

'is forgiven oddly? hard to stop it' is the wordplay.
I cannot quite see how this works, but
'is' is present in the answer.
'hard' could be 'h' (abbreviation used in pencil classifications) and 'h' is found in the answer.
an anagram of 'forgiven' is 'overfing' which is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Times.

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