Value-Added Models of Teacher Effects

Abstract

The ability of teachers to raise student academic achievement varies but the reasons are not always clear. Differences among teachers account for an important portion of the achievement differences among students. Teacher effects exist, they are measurable and significant, and they have a cumulative impact on student performance. The differences between teachers can be quantified as "teacher effects" using value-added models. Value-added models attempt to measure how much value a teacher, or school, has added to a student's learning. The models provide a statistical estimate of teacher or school effectiveness by decomposing the variance in student test scores into portions that are explained by students and portions that are assumed to be related to the current teacher and school. Teacher effects are based on test scores. They are the variance that remains unexplained after a number of sources of variability over which a teacher and school have no control have been taken into account (ex. student characteristics and background). These variations in student achievement gains (residuals) are interpreted to be a measure of teacher effectiveness. Differences between teachers are the variation in adjusted student achievement gains between classrooms. Over 70 years of research into teacher effectiveness utilizes student learning outcomes as the significant indicator of effectiveness (Campbell, Kyriakides, Muijs, & Robinson, 2003). Much of this research on teacher effectiveness is directed at improving the preparation of teachers and their development for the purpose of improving student learning. Public policy has increasingly focused on the skill and knowledge development of teachers in order to promote a higher level of student achievement. The logic is that if teacher quality improves through certification standards and professional development, student achievement will follow. The conundrum is that teacher qualifications are not the same as teacher quality. To illustrate, recent studies have not found that California or Texas State Certifications or the national teaching certifications (NBPTS) are producing increased teacher effectiveness