Excellent article on the fallacy of such schemes, from Education Week
http://www.edweek.org/ew/articles/2010/02/10/21snider.h29.html?tkn=WULFenQGhor36vh6Ik%2FtDmx33IFioR338KJ1&cmp=clp-edweek<snip> First, when a student fails to flourish, it is rarely the result of one party. Rather, it tends to be a confluence of confounding factors, often involving parents, teachers, administrators, politicians, neighborhoods, and even the student himself. If we could collect data that allowed us to parse out these influences accurately, then we might be able to hold not just teachers but all parties responsible. At present, however, we are light-years away from even understanding how to collect such data.
Second, learning is not always, or easily, captured by high-stakes tests. A student’s performance on a given day reflects a whole lot more than what his teacher has or hasn’t taught him.
<snip> The short answer to both questions is because our current data systems are a complete mess. We tend to collect the wrong kinds of data, partly to save money and partly because we’re not all that good at statistical analysis.