I taught high school for over 30 years, the last 20+ at Francis Lewis HS in Queens. I was pretty good at reaching the students others could not and was always given the most challenging ones. I even volunteered to take students from other teachers in hope of getting them through. I say I was pretty good, not great and my passing results were usually in the 80th percentile although one semester I did get 27 out of 28 to pass the algebra 1 regents and graduate. While some might say my statistics were good, they were usually the worst in the department. No one seemed to care about the population I taught and the previous history of these students. Stats were all that mattered.
Today there is a mad rush mid semester to drop any students who might fail the regents. No one wants to take a chance on helping them because the students failure translates into the teacher's evaluation. These students then take non regents math and go on to college where they are ill prepared for success. Even if they stayed behind and failed, they would have seen material and been better prepared for the future. And, many who were dropped might have passed, if not the first time then the second.
Teachers should be evaluated. I worked for a Principal who walked the halls daily and knew what was going on in each classroom. I worked for an AP (30+ years ago-not at Francis Lewis) who wrote 5 page observations, commenting on every little thing and giving complements and constructive criticism. She knew who was good and who should not be teaching and acted accordingly.
Teaching is an art and art cannot be evaluated with test scores.