First the good news. There's a growing consensus that the quality of teachers and teaching is a major factor--some would say the most important school-based factor--in the quality of student learning. In sum (and this comes as no surprise to the teaching profession), good teaching matters. The bad news is that, in this highly charged climate of data-driven accountability, teacher effectiveness and compensation are increasingly being tied to student scores on standardized tests. This paper presents several arguments that merit pay is another in a series of market-based education policy reforms that doesn't stand up to scrutiny, one being driven by ideology rather than sound research.