Parents don't have to "believe" teachers are effective; they can see the results for themselves and judge them. My parents had no problem telling which of my teachers were actually teaching me things and which were just boring me to death in class.

As for "rigorous", the whole point of the comment I responded to was that there are no "rigorous" third-party measures of teacher effectiveness. That's the "problem" that all these experts have been struggling unsuccessfully to solve for decades. The reason they can't solve it is that as they have conceived the "problem", it's not solvable. The people in a position to judge the effectiveness of teachers are the people who directly observe the impact of their teaching. Third-party "experts" can't do that.

Not all parents are that involved, and a kid being bored in class isn't necessarily the teacher's fault.

Then that's the root problem that needs to be fixed, and trying to invent ways for third party "experts" to "measure teacher effectiveness" won't help.

> a kid being bored in class isn't necessarily the teacher's fault

It might not be that individual teacher's fault, true; the kid might just be in the wrong class. But it still means there's a teaching problem.