My sense is that it's less of a problem now than it was in the past. As others have said, a large number of people in the trades have high school or less. Right now, however, almost everyone graduates from high school. Going forward, my sense is that lack of high school education is likely to be far less of a problem than it was historically, when people found their way into the trades after dropping out of high school, say.
I would comment and agree that having a high school education—and there is good evidence of this—contributes to the ability to pass the exams. The exams have a fairly substantial literacy component in them, and we've discovered, particularly in the carpentry exams, that a large part is basic high school mathematics. If you don't have high school mathematics, you will struggle with that exam. That's true for trade qualifiers.
Apprentices have much less of a problem. My sense is that going forward, as I said, that problem is likely to largely resolve itself.