Teacher had to be charitable (6)
I believe the answer is:
donate
'be charitable' is the definition.
(I've seen this in another clue)
'teacher had' is the wordplay.
'teacher' becomes 'don' (don is a kind of teacher).
'had' becomes 'ate' (e.g. I had an ice cream).
'don'+'ate'='DONATE'
'to' is the link.
(Other definitions for donate that I've seen before include "Give (transplant organ)" , "Give as gift, say blood" , "Make an offer" , "Contribute charitably" , "Make a contribution" .)