College group has three miles on climber (3,6)
I believe the answer is:
ivy league
'college group' is the definition.
(prestigious group of US colleges)
'three miles on climber' is the wordplay.
'three miles' becomes 'league' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'climber' becomes 'ivy' (ivy is a climbing plant).
'league' put after 'ivy' is 'IVY LEAGUE'.
'has' acts as a link.
(Other definitions for ivy league that I've seen before include "Group of US elite universities" , "Eight prestigious US universities" , "Brown, Columbia, Cornell, Dartmouth, Harvard, Pennsylvania, Princeton and Yale" , "Group of US universities of high prestige" , "academic grouping" .)