Number of pupils in college yesterday (4)

I believe the answer is:

eyes

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'number of pupils' is the definition.
The answer and definition can be both body parts as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'in college yesterday' is the wordplay.
'in' says the answer is hidden in the clue.
'EYES' is hidden within 'college yesterday'.

Can you help me to learn more?

(Other definitions for eyes that I've seen before include "Peacock's tail markings" , "Peepers" , "Looks at carefully" , "Witnesses" , "Marks on potatoes" .)

I've seen this clue in The Irish News.

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