I have a couple of brief comments.
Acknowledging what John has just said, the reality is that in most trades there is substantial financial payoff to certification, and that can be demonstrated. It's not clear that's obvious to people, and it's not true in some trades, by the way. An apprentice hairstylist, for example, does just as well as a certified hairstylist in that respect, but that's not true in other trades.
Going back to the main point about schools, my comments should not be construed as being that we shouldn't expose people to the trades and technologies in schools. Indeed, programs of that nature are quite important.
What I would argue against in particular is emulating the German model, just as the Germans are beginning to reconsider it themselves. The effect of a model like the German model is to stream people very early into programs that they can't get out of. In other words, if you want to go to university at age 14 in Germany and you find yourself in the trades—the dual system—you're precluded from doing so. The Germans themselves are rethinking that on the grounds that their overall performance in international programs in high school are mediocre at best, and their concern is that they put too much emphasis on the trade side.
So I would argue for exposure to the trades by all means, but not explicit streaming in that direction.