Teacher sitting and hatching a plan (13)

I believe the answer is:

masterminding

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'hatching a plan' is the definition.
Although both the answer and definition are present participle verbs, I can't see how one could define the other.

'teacher sitting' is the wordplay.
'teacher' becomes 'master' (I've seen this before).
'sitting' becomes 'minding' (I can't justify this - if you can you should believe this answer much more).
'master'+'minding'='MASTERMINDING'

'and' acts as a link.

Can you help me to learn more?

(Another definition for masterminding that I've seen is " Organising".)

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

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