We can think of value - added
estimates as measuring three components: (1) true
teaching effectiveness that persists across years; (2) true
effectiveness that varies from year to year; and (3) measurement error.
The researchers assert that these factors can create faulty
estimates of teachers»
effectiveness, as well as disincentives for teachers to
teach the students with the greatest needs (Darling - Hammond, Amrein - Beardsley, Haertel, & Rothstein, 2011, p. 3).