Be leader of school group, finding source of river (10)

I believe the answer is:

headstream

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'source of river' is the definition.
'headstream' can be an answer for 'source' (thesaurus). I'm unsure of the 'of river' bit.

'be leader of school group' is the wordplay.
'be leader of school' becomes 'head' (I am not sure about this - if you are sure you should believe this answer much more).
'group' becomes 'stream' (stream is a kind of group).
'head'+'stream'='HEADSTREAM'

'finding' acts as a link.

Can you help me to learn more?

(Another definition for headstream that I've seen is " Current".)

I've seen this clue in The Times.

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