Current students of similar ability on display (9)
I believe the answer is:
airstream
'current' is the definition.
(a current of air)
'students of similar ability on display' is the wordplay.
'students of similar ability' becomes 'stream' (stream can mean a class of similarly able pupils).
'on' means one lot of letters go next to another.
'display' becomes 'air' (air can mean to display or show something).
'stream' after 'air' is 'AIRSTREAM'.
(Other definitions for airstream that I've seen before include "wash" , "Jet" , "Atmospheric current" , "What might waft" , "Wind at high altitude" .)