[Principled]

A Texas art teacher has no academic effect on any student's TAKS test scores.

I strongly disagree with this. But before I go further, let me say that I agree with your assertion that assessment of teacher value is not gonna work for so many reasons.

[Clara Lou]

I strongly disagree with this.
I'm not sure exactly what you mean by this or what you know about Texas. Here's my thinking: If teach high school Spanish-I, I teach absolutely nothing related to the state TAKS math or science tests. It's possible that in a unit I might touch on something vaguely related to TAKS social studies, or I might reinforce something for TAKS English [parts of speech, point of view]-- it's stricly coincidental and depends on the TAKS level test the student is taking. Any relationship between my students' TAKS scores and the academic content in my classroom is a forced one. This is why I cannot figure out how I could possibly assessed a reward based on student performance.