"Merit pay" for teachers sounds good, but is not fair or effective.

Houston just voted to link teachers' pay to their students test scores. Teachers responded with mixed reactions. Everybody's got an opinion. But for me, I just want to understand how it can be fair and effective.

A major criticism of relying on test scores is that they can easily be misleading. First off, each group of students are different. You might have a brilliant class go through one year and a struggling class go through the next year. Obviously, the scores will differ. In those cases, the teacher will simply get extra money because of the kids' talents not necessarily their own (the same quality of teaching will still get widely varied scores). This will not "incentivise" better teaching, but stronger lobbying for the better students. It will make education more political, and in all the worst ways.

If testing is done in staggered years, how do we know which teachers contributed what? If Johnny does well on his 4th grade testing, was it the 4th grade teacher or the 1st-3rd grade teachers who did had the most impact? One teacher shouldn't get all the credit (or blame) for the work of everybody else.

But it gets murkier at the higher levels. Should the history teacher be penalized because Johnny can't read on a high school level? Some high school teachers are hamstrung by students who are not prepared to be there. So many high school teachers will be "incentivized" to turn to the in-office politics of cherry picking the best students to get the rewards (and avoid shame), which tells us nothing of that teacher's ability to teach. There are already too many "good ol' boy" networks in public administration. Nothing is accomplished by adding more.

Also, not every teacher within a department has the same quality of students. Not every science teacher gets to teach the Advance Placement classes (even if every teacher is equally gifted, there's just not enough AP classes for everybody). And who's in the AP classes? The school's best students in that subject. So a great teacher who's assigned regular or sub-par students--where they are arguably needed most--will be penalized instead of rewarded.

And I won't go into the disparities from school to school, such as magnet schools (which are a good thing) who get the best students and leave other schools with lower performers. And how unfair it is to compare rural "catch-all" schools with urban specialized schools?

The media insists on painting resistance to "merit pay" as teachers wanting to avoid accountability. By and large, this is a falsehood. Good teachers would dearly love to be rewarded, and see bad teachers get their come uppance. But "merit pay" based on test scores--as typically proposed--will not accomplish this.

The only way would be to treat each district as a whole, and by tracking students longitudinally through the whole system from kindergarten to high school graduation. No teacher or school succeeds or fails in a vacuum.