The governor of New York recently proposed that 50% of teachers evaluations be based on the results of standardized tests. I’m not going to go into great detail about how much of fundamental misunderstanding of the purpose of standardized tests that is. The short version is that standardized tests give the most useful information when disaggregated, so for example looking at a district by district sample, or by selecting randomized classrooms from the entire state/province to give an overall picture. Other people have explained what a problem it is to hold teachers responsible for things they don’t have full control over. I’m not going to go into that today. Instead I’m going to focus on the labour market.