Teacher Quality and Value-Added Models
Teacher quality is the single most important school-based determinant of student achievement.
Overview
The consensus in education economics is that teacher quality is the most important school-based determinant of student achievement. Unlike traditional research that measures quality through credentials, the modern causal literature defines teacher quality almost exclusively as value-added — the marginal contribution a specific teacher makes to a student's academic growth, controlling for prior achievement. Observable credentials such as master's degrees and certification status explain less than 5% of the true variance in teacher effectiveness.
The Value-Added Debate
Rivkin, Hanushek, and Kain (2005) and Rockoff (2004) demonstrated that the standard deviation of teacher value-added effects on student test scores is approximately d = 0.10–0.15. Chetty, Friedman, and Rockoff (2014) provided the most influential defense of VAMs, finding that replacing a bottom-5% teacher with an average teacher raises the lifetime earnings of a single classroom by approximately $250,000. However, Rothstein (2010) demonstrated that standard VAMs fail falsification tests — teachers appear to affect students' prior test scores, indicating significant non-random sorting. The American Statistical Association issued a formal statement in 2014 advising against using VAMs as the sole basis for high-stakes teacher evaluation.
Non-Cognitive Teacher Effects
Jackson (2018) found that teachers have substantial effects on non-cognitive outcomes — attendance, behavior, and course grades — and that these non-test-score effects predict high school graduation and college-going even when a teacher's test-score value-added is low. Crucially, a teacher's non-test-score value-added is weakly correlated with their test-score value-added (r ≈ 0.15–0.30), meaning that schools evaluating teachers solely on test scores miss a substantial portion of what teachers contribute to student development.
Teacher Labor Market and Retention
Teacher salaries in the US are compressed relative to other professions requiring similar education, and the salary structure does not reward effectiveness. High-performing teachers earn roughly the same as low-performing teachers with similar experience and credentials. Evidence on performance pay is mixed: some studies find positive effects (Fryer, 2014), while others find that poorly designed incentive structures can crowd out intrinsic motivation.
While teacher quality matters immensely, our ability to measure it precisely enough for high-stakes personnel decisions remains highly contested. The appropriate policy response may be to invest heavily in teacher recruitment, preparation, and mentoring rather than aggressive termination of low-performing teachers based on imprecise VAM estimates.
Key Papers
- Blazar (2018)Validating Teacher Effects on Students' Attitudes and Behaviors: Evidence from Random Assignment of Teachers to Students
- Chetty & Friedman & Rockoff (2014)Measuring the Impacts of Teachers I: Evaluating Bias in Teacher Value-Added Estimates
- Chetty & Friedman & Rockoff (2014)Measuring the Impacts of Teachers II: Teacher Value-Added and Student Outcomes in Adulthood
- Jackson (2018)What Do Test Scores Miss? The Importance of Teacher Effects on Non-Test Score Outcomes
- Rivkin & Hanushek & Kain (2005)Teachers, Schools, and Academic Achievement
- Rockoff (2004)The Impact of Individual Teachers on Student Achievement: Evidence from Panel Data
- Rothstein (2010)Teacher Quality in Educational Production: Tracking, Decay, and Student Achievement