E D U C AT I O N
Value-Added Modeling 101
Using Student Test Scores to Help Measure
Teaching Effectiveness
Value-added models, or VAMs, attempt to measure a teacher’s impact on student
achievement—that is, the value he or she adds—apart from other factors that affect
achievement, such as individual ability, family environment, past schooling, and the
influence of peers.
VAMs attempt to estimate a teacher’s contribution to students’
progress over time.
The goal of VAMs is to allow educators and policymakers to make applesto-apples comparisons among teachers in terms of how much content their
students learn each year, regardless of the students’ characteristics. This
means focusing not on how students test at a single point in time but rather
on how much improvement they make from one testing period to the next.
VAMs use statistical methods to account for students’
prior characteristics.
There is no single VAM that all researchers use, but all of the models account
in some way for the prior test scores of a teacher’s students. One common
VAM method works like this: Mr. Johnson teaches 6th grade math. To estimate his added value, statisticians obtain the 4th and 5th grade test scores
of all his students, as well as information about their backgrounds (such as
whether they were in a gifted program or a special education program).
Those data are used to predict what the students’ 6th grade math scores
will be. Caryn and Darren are students in Mr. Johnson’s class. Caryn’s actual
score on the 6th grade test is seven points higher than predicted; Darren’s is
two points lower. Mr. Johnson’s value-added estimate is the average of the
differences between the actual and predicted scores of Caryn, Darren, and
the rest of the class.
Value-added estimates enable relative judgments but are not
absolute indicators of effectiveness.
Because VAMs adjust for students’ prior performance and background
characteristics, one teacher’s value-added estimate can be compared with
another’s. For this reason, VAMs are sometimes used to rank teachers
who teach the same subject and grade level. However, there is no specific
number that identifies “acceptable” performance.
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