Student assessment nonparticipation (or opt out) has increased substantially in K-12 schools in states across the country. This increase in opt out has the potential to impact achievement and growth measures used for educator and institutional accountability. This simulation study investigates the extent to which value-added measures of teacher quality are impacted as a result of varying degrees of opt out, as well as various types of nonrandom opt out. Results show that the magnitude of opt

more »

... has a greater impact on stability of value-added estimates than the type of nonrandom opt out patterns simulated in this study, with root mean square differences in value-added estimates and standard errors increasing as the magnitude increased. In addition, classification agreement decreased as magnitude increased. Finally, one type of opt out, where the highest achieving students in the highest achieving classrooms did not participate, appeared to have more of an impact on stability than the other types of opt out in this study.