Value added
Value added scores assume that students are randomly assigned to teachers. In reality students are rarely randomly assigned to teachers or to schools. According to economist and professor, Dr. Jesse M. Rothstein of University of California, Berkeley, "Non-random assignment of students to teachers can bias value added estimates of teachers’ causal effects." The issue of possible bias with the use of value added measures has been the subject of considerable recent study, and other researchers reach the conclusion that value added measures do provide good estimates of teacher effectiveness. See, for example, the recent work of the Measures of Effective Teaching project and the analysis of how value added measures relate to future incomes by Professor Raj Chetty of Harvard and his colleagues.