Teacher of poor stream (6)
I believe the answer is:
master
'teacher' is the definition.
(I've seen this before)
'poor stream' is the wordplay.
'poor' indicates an anagram.
'stream' with letters rearranged gives 'MASTER'.
'of' acts as a link.
(Other definitions for master that I've seen before include "Virtuoso" , "Subdue, win over" , "controlling" , "Dominate" , "Male teacher or ship's captain" .)