Phrase to mean a 'bad teacher'/'poor teacher'
Solution 1:
I would suggest amateur.
A person unskilled in or having only a superficial knowledge of a subject or activity. (TFT)
A person who is contemptibly inept at a particular activity. (ODO)
That bunch of stumbling amateurs.
This word fits into your sentence:
Mark Carlson is an amateur, he cannot teach a thing.