The article addresses those concerns: 'Merit should be defined in terms of the improvement that teachers deliver to their students over the course of a school

The article addresses those concerns: 'Merit should be defined in terms of the improvement that teachers deliver to their students over the course of a school year. This framing controls for other variables affecting student performance and ensures that teachers in wealthy school districts aren’t rewarded because their students come in with an advantage.' 'The bonuses created an incentive for highly rated teachers to move to disadvantaged schools, and within two years students were performing at close to the city’s average level.'