Assembles unruly pupils around end of June (5,2)

I believe the answer is:

piles up

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'assembles' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot understand how they can define each other.

'unruly pupils around end of june' is the wordplay.
'unruly' is an anagram indicator.
'around end of' suggests the final letters.
The final letter of 'june' is 'e'.
'pupils'+'e'='pupilse'
'pupilse' with letters rearranged gives 'PILES UP'.

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I've seen this clue in The Daily Mail.

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