why merit pay merits skepticism

Ryan of I Thought a Think explains.

These are the stories that will be passed around like folk tales when some district here in Washington takes the leap and tries it, and these are the problems that merit pay supporters don’t have ready answers to. Why would teachers risk public embarrassment for $100? How can we distinguish between the luck of the draw and truly effective teaching when it comes to evaluating the growth of a classroom?

Nobody really knows. Except me.