Master's current form (6)
I believe the answer is:
stream
'form' is the definition.
(both can mean a group of pupils)
'master's current' is the wordplay.
'master' can be anagrammed to 'STREAM'.
But, I'm unsure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for stream that I've seen before include "group of pupils split by ability" , "Natural body of running water" , "'Brook, runnel (6)'" , "Flock" , "Constant flow of liquid" .)