Colleague’s wife teacher stumbled over first (9)
I believe the answer is:
bedfellow
'colleague's' is the definition.
(both can mean an associate)
'teacher stumbled over first' is the wordplay.
'teacher' becomes 'BEd' (bachelor of education).
'stumbled over first' becomes 'fellow' (I can't justify this - if you can you should give a lot more credence to this answer).
'bed'+'fellow'='BEDFELLOW'
'wife' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
(Other definitions for bedfellow that I've seen before include "Person slept with" , "Colleague" , "Close associate or partner" , "Mate" , "Partner (in the boudoir?)" .)