I don't know much, but I'm always for sticking it to Rahm Emanuel.
The idea of merit pay sounds good in theory, but it's dicey at best in practice. How are you going to determine if a teacher is doing a good job? How do you isolate a teacher's performance from the myriad other factors that go into a student's success that a teacher has no control over? And so on.
Each district is different, yet, every teacher is evaluated annually, usually by their principal. Principals are in the building every day and over the course of 170+ school days it becomes clear who are the most effective teachers. I do not believe merit pay is a fix for anything wrong in education. Schools ditricts are so diverse; urban/rural, big/small, wealthy/poor, I have no clue how anyone would think they could administer education nationally.
As the spouse of a teacher in Ohio, I pay some attention to this issue and I have mixed feelings. I'm a taxpayer, too. But when it comes to merit pay, my corporate experience tells me that the education "associations" and their press agents are very good at blowing smoke up the a^%$# of their members and the public.
You want performance metrics that are measurable? How about continuing education achievements, professionalism, work attendance, (School) community activism, innovation, adaptation, "works well with others" (this one is HUGE). That's a pretty good list in my world and we haven't gotten to the daily work results part yet. It's doable, it just isn't going to be popular because the idea of step raises and early retirement is so engrained in this system. BTW, my teacher-wife, who lost her job due to the selfish interests of a union run by "lifers" is 100% on board with the merit pay / reward system. She just doesn't have a job anymore.