Former pupils gather pine to make shapes (7)

I believe the answer is:

oblongs

'shapes' is the definition.
(oblong is a kind of shape)

'former pupils gather pine' is the wordplay.
'former pupils' becomes 'OBs' (Old Boy can mean a graduate of a private school).
'gather' means one lot of letters goes inside another.
'pine' becomes 'long' (to pine for something is to long for it).
'obs' going around 'long' is 'OBLONGS'.

'to make' acts as a link.

(Another definition for oblongs that I've seen is " Rectangles".)

I've seen this clue in The Guardian.

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