NP on merit pay

Kate Tennier's piece in Friday's National Post caught the eye as she advocates for merit pay for teachers. Tennier's own website makes for some interesting reading, as she puts together the pieces of a position on increased parental involvement in education and explains a graduated scale of home schooling. A change advocate who says our classrooms should change because almost everything else has over the last 40 years-- a statement that leads me to believe Tennier hasn't witnessed the machinations of a real classroom in that long.
From the NP piece:

Teacher merit pay exists in Canada. Every time a parent chooses a private school or tutor for their child, the pay these educators receive is based on “merit.” I know of two Toronto teachers who founded small but thriving schools at the behest of parents — parents who determined that these teachers “deserved” the fees being paid to them.
We even have government sanctioned merit pay now: Alberta’s culture of educational choice sees state dollars flowing to those institutions that parents have decided “merit” their child’s attendance. Subsidies for childcare mean that parents use government dollars to choose the adult they want their child to be with based on the merit that person brings to their child’s life. And, the government’s matching post-secondary tuition grants mean it is funding only those institutions students have deemed meritorious of their own dollars.
Everywhere educational choice exists, the remuneration teachers receive is based on true worth because it is a “worth” determined by the learner. When we expand this choice to all levels of learning, the pay teachers receive will not only be fair but will become a catalyst for further wide-reaching educational reforms.

She closes the piece with these three paragraphs, but the intent here is to suggest that all teachers in the publicly funded system should receive merit pay. Earlier in the piece, she uses examples from public schools in the U.S. where teachers are bonused for their students' achievement in testing and for increasing enrolment.
First, I don't agree with the analysis that merit pay exists in Canada due to the availability of private schools, tutors, etc. A private school teacher is rarely paid more because they're better or worse at teaching than their peers. I would hazard guessing many private schools aren't rolling in that much money and pay their teachers less than the public systems do (I know this to be the case in a few schools locally, but most are faith-based around here). Similarly, a voucher or charter school likely doesn't pay better / worse given the number of parents who choose those schools for their children. The kids would still be in a "system" if they weren't attending the charter school and I could just as easily argue those "merited" teachers would be teaching in other schools as a result.
Tennier seems to have confused merit with choice. Parental choice is what has created and, possibly, allowed those teachers to benefit from those options.
A great part of my difficulty with this is defining what merits pay in education. Kids aren't widgets. They're not an automotive part being pumped out of a factory where the faster the employee works and the higher-quality pieces they manufacture the more money they make for their employer, a situation where that person might merit a share of the increased profits.
Perhaps in other areas like the U.S., where schools' performance has a very real impact on grants (do better and you earn more) and poor performance can lead to closure this argument would carry more weight. We're not there yet, I would hope, in Canada and specifically in Ontario.