Crossword Genius

Work on the school map somehow: it’s used to examine pupils (14)

Ross

I believe the answer is:

ophthalmoscope

I'm a little stuck... Click here to teach me more about this clue!

'used to examine pupils' is the definition.
I can't tell whether this defines the answer.

'work on the school map somehow' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'somehow' is an anagram indicator.
'the'+'school'+'map'='theschoolmap'
'theschoolmap' is an anagram of 'hthalmoscope'.
'op'+'hthalmoscope'='OPHTHALMOSCOPE'

'it's' is the link.

Can you help me to learn more?

(Other definitions for ophthalmoscope that I've seen before include "Optical instrument" , "Instrument for inspecting the retina and other eye parts" .)

I've seen this clue in The Times.
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