Form stream for teacher (6)
I believe the answer is:
master
'teacher' is the definition.
(I've seen this before)
'form stream' is the wordplay.
'form' indicates an anagram.
'stream' is an anagram of 'MASTER'.
'for' is the link.
(Other definitions for master that I've seen before include "Teacher to gain control" , "Overcome; great artist" , "Craftsperson of great skill" , "Male teacher or ship's captain" , "One has consummate skill" .)