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Misconception: Teacher value-added estimates are not reliable enough to be used in high-stakes decisions.

Many studies on teacher estimates focus on single-year estimates, some of which are derived from simplistic value-added or growth models. However, TVAAS teacher value-added estimates are based on a robust statistical approach and report a multiple-year average whenever available. The approach provides very reliable teacher estimates, which educators can use for a variety of educational and policy decisions.

TVAAS in Theory

Many critics use the repeatability of teacher value-added estimates as a proxy for their reliability. However, "perfect" repeatability is not the goal as some year-to-year variation among individual teachers' estimates is to be expected. Cohorts of students change every year, and teachers might be more effective with one group than another. Standards or assessments might change from one year to the next. However, the presence of strong reliability indicates that teachers' value-added estimates are related to their consistent skills and are not generated primarily from a random component.

SAS reviewed value-added estimates over the past two decades using data from another state that uses methodology similar to TVAAS and found that:

  • Highly effective teachers are very likely to remain effective. Teachers identified as having students who exceed expected growth after their first three years of teaching were extremely likely to have similar growth with their students three years into the future (about 95% were either average or above average in their students' growth).
  • Less effective teachers might improve over time. For the teachers identified as having students who do not meet expected growth based on three-year estimates, approximately half of them will continue to have students with similar growth three years later.

This has enormous implications in terms of the usefulness of the reporting provided by TVAAS such that educators and policymakers can rely on the teacher estimates to inform their decisions.

TVAAS in Practice

In 2012, the Tennessee Department of Education reported to the legislature that less than 1% of Tennessee teachers moved from Level 5 (most effective) to Level 1 (least effective) from one year to the next based on three-year TVAAS teacher estimates.

In other words, in using a robust and reliable statistical approach for teacher estimates, such as TVAAS, Tennessee educators and policymakers can build insightful policies customized to the teachers in their schools, systems, and state.