Section of society running study group (7,5)

I believe the answer is:

working class

'section of society' is the definition.
(social class)

'running study group' is the wordplay.
'running' becomes 'working' (synonyms).
'study group' becomes 'class' (group of people studying together).
'working'+'class'='WORKING-CLASS'

(Other definitions for working class that I've seen before include "Manual or unskilled employees in general" , "seminar" , "Common" , "Blue-collar" , "Labour group" .)

I've seen this clue in The Telegraph.

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