Chesterton's fence applies. The seniority system has serious drawbacks, but it has the advantage of being simple and difficult to game. It limits the damage caused to organizations by manipulators who would use more sophisticated systems to rig the workforce for personal or political advantage. It means that the average Ontario kid will encounter an average and well-distributed selection of both good and horrible teachers. Ignore the value of that at your peril.

My kids are+were in the Ontario system. I pay attention to their quality of education. Across my parenting circles there are kids in every type of school and program conceivable. I could afford to send mine to private school if I thought it necessary. One of my kids is now at a competitive university with smart and hardworking kids from across the globe and he was well-prepared by his high school. In my opinion we are getting a good distribution of good outcomes, should consider ourselves lucky, and be careful not to take our system for granted, or accidentally break it through ideology or ignorance. And almost no one knows what works and what doesn't, but I believe that part of what works is treating teaching as the serious and challenging profession that it is, and letting them get on with it. You know, pretty much what we want from our stakeholders?

I am very much of the opinion that we must be all-in on one public school system, with explicit objectives: providing a good education, underpinning social cohesion, encouraging individual diversity, seeking equality of opportunity.

(I am not a teacher or in any union, and neither is anyone in my family.)