Is it exactly 6 months? A little over 6 months or a little under 6 months?
http://www.cic.gc.ca/english/study/study-who.asp said:
In some cases, you do not require a study permit to go to school in Canada.
* If you wish to study in a short-term course or program
You do not need a study permit if you plan to take a course or program in Canada that lasts six months or less. You must complete the course or program within the period authorized for your stay in Canada.
So if he's authorized to stay in Canada as a foreign worker or anything else until the course is done or longer and the course is 6 months or shorter, not longer, then he doesn't need a study permit. Otherwise, he will have to apply for a study permit which means he can no longer work.