Choose independent state helping pupils work? (7)

I believe the answer is:

optical

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'choose independent state helping pupils work?' is the definition.
I can't tell whether this defines the answer.

'choose independent state' is the wordplay.
'choose' becomes 'opt' (I've seen this before).
'independent' becomes 'i'.
'state' becomes 'cal' (I've seen this in other clues).
'opt'+'i'+'cal'='OPTICAL'

Can you help me to learn more?

(Other definitions for optical that I've seen before include "Working with light" , "Involving light" , "Using visible light" , "Sort of illusion" , "Concerning sight" .)

I've seen this clue in The Guardian.

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