- Value-added measures for principals have many of the same problems that value-added measures for teachers do, such as imprecision and questions about whether important outcomes are captured by the test on which the measures are based.
- While most measures of teachers’ value-added and schools’ value-added are based on a shared conception of the effects that teachers and schools have on their students, value-added measures for principals can vary in their underlying logic.
- The underlying logic on which the value-added measure is based matters a lot in practice.
- Evaluation models based on school effectiveness, which measure student test- score gains, tend not to be correlated at all with models based on school improvement, which measure changes in student test-score gains.
- The choice of model also changes the magnitude of the impact that principals appear to have on student outcomes.
- Estimates of principal effectiveness that are based on school effectiveness can be calculated for most principals. But estimates that are based on school effectiveness relative to the effectiveness of other principals who have served at the same school or estimates that are based on school improvement have stricter data requirements and, as a result, cover fewer principals.
- Models that assume that most of school effectiveness is attributable to the principal are more consistent with other measures of principal effectiveness, such as evaluations by the district. However, it is not clear whether these other measures are themselves accurate assessments.
- There is little empirical evidence on the advantages or disadvantages of using value-added measures to evaluate principals.