Schoolchild making a light admission? (5)

I believe the answer is:

pupil

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'schoolchild' is the definition.
(synonyms)

I don't understand the rest of the clue.

(Other definitions for pupil that I've seen before include "Aperture in an eye" , "Schoolboy or eye part" , "One studying" , "feature in "Observer"?" , "Schoolchild; part of eye" .)

I've seen this clue in the Evening Standard.

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