Step 1: Sean Corcoran, an economist at New York University, studied the teacher evaluation systems in New York City and Houston.
Step 2: Sean Corcoran found that the mean “margin of error” of a teacher in New York City was 28 points give or take.
Step 3: The value-added scores fluctuate throughout the years because teachers receive different rankings yearly, (Ravitch 270-271).
Step 4: Because of the fluctuating rates between years, predicting the rating one will receive is nearly impossible because it is unlikely they will get the same rank ( Ravitch 270-271).
Step 5: The technique used to measure an individual teacher based on “growth models” has proven to be inefficient because there is too much room for error (Ravitch 270-271).
Diane Ravitch, The Death and Life of the Great American School System (New York: Basic Books, 2011), pp.270-271.