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Recent education reform efforts commonly aim at improving teacher effectiveness. One study of three large districts finds that they spent approximately $18,000 for professional development for each teacher each year. Numerous education agencies, such as the District of Columbia Public Schools with its IMPACT effectiveness system for school-based personnel, and the state of Tennessee with its Tennessee Educator Acceleration Model, have invested substantial resources in teacher evaluation and feedback.

These policies arose, at least in part, from the recognition that teachers affect not only student learning in the short-run, but also long-run outcomes such as college attendance and earnings as adults. A recent study following more than two million students estimated that having a teacher in grades four through eight with average effectiveness, instead of one who is among the five percent least effective, would increase a students’ lifetime income by more than $250,000. Teachers also affect the likelihood that a student attends any college, attends a higher-ranked college, does not have children as a teenager, and saves more for retirement.

Most of the researchers examining the effects of teachers on student test performance have concluded that math teachers have a greater effect on students’ performance on math exams than English language arts teachers have on students’ performance on English exams. For example, studies in North Carolina and New York City found that math teachers had approximately a 35 percent greater impact on test scores in their field than did English teachers.

Nonetheless, the research on the long-term effects of teachers finds that English teachers have at least as much of an effect as math teachers. For example, that same study following 2.5 million students found that an English teacher who raises students’ reading test scores by the same amount as a math teacher raises students’ math test scores has an impact on long-term life outcomes approximately 1.7 times that of the math teacher. Even though, on average, English teachers don’t increase English language arts test scores as much as math teachers increase math scores, English teachers have as strong an effect on students’ later lives.