Teacher Evaluation in Washington, D.C.
Teacher accountability is nowhere more on display than in Washington, D.C. schools. Under IMPACT, which began in 2012, teachers receive a single score ranging from 100 to 400 points ("A Lasting Impact," Education Next, Fall 2017). It is based on classroom observations, measures of student learning, and commitment to the school community.
There are heavy consequences, both negative and positive, for teachers. Those who get a very low score are dismissed, while those with a high score get a bonus of up to $25,000 for each year they receive that rating. Reformers laud the system, saying that it creates great incentives for teachers to quit (the former) and for teachers just below the top threshold to make additional effort to clear the bar (the latter). Perhaps, as a direct result, the D.C. school system was named the fastest improving large urban system in the country, according to the National Assessment of Educational Progress.
All this sounds a bit too good to be true. Are students randomly assigned to teachers? That's a crucial factor in determining the effectiveness of any teacher. So much of success is determined by the students a teacher happens to inherit. Give a bad teacher a classful of Talmudic scholars, and the teacher is going to shine. Conversely, give a good teacher a classful of delinquents and the teacher is going to flop. This comes under the heading of "bias in individual teacher effect estimates."
I saw that happen time and again when I taught in the Los Angeles Unified School District. Unless students are randomly assigned, which is rarely - if ever - the case, valid inferences cannot be drawn. There is a grapevine in every school that tends to be followed when assigning students. So before assuming that IMPACT is, in fact, the solution, I'd like to know about how students are assigned.