The paper puts in question the value added of individual teacher on a specific class - which is not really a very surprising finding, given that the incentive p

The paper puts in question the value added of individual teacher on a specific class - which is not really a very surprising finding, given that the incentive payments in the US are known to push "good" teachers to take "good" classes if they can get them (not sure if this applies in NY but it's a common critique of the incentive systems - the worst students get even worse services and outcomes as pre- and post-intervention results are really difficult to measure and compare if the only data are really badly done central exams). At system level however the data is very robust: in a developed education system the best you can do is to give autonomy to schools and teachers, assure some kind of accountability (not necessarily exams, but eg European-style 'supportive' inspection) and strengthening teachers through training and support is the most effective education intervention, except maybe for free school meals.