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.
A forthcoming study using data from urban areas in two states sheds light on why English teachers have these strong effects even though their effects on current year test scores are not as strong.  The benefits of good English teachers are seen in students’ achievement in future years, not only in English, but in other subjects as well. The study distinguishes the persistent effects that teachers have in their own subject—English teachers on students’ later English test performance and math teachers on students’ later math test performance—from cross-subject effects in which English teachers in one year can affect math performance in subsequent years and math teachers in one year can affect math performance in a subsequent year. While the effects that math and English teachers have on students’ test scores in the year that they have them similarly persists in their own subject in subsequent years, the gains in English scores due to English teachers have far greater effects on students’ subsequent math performance than the gains in math scores due to math teachers have on students’ subsequent English performance.
In fact, in some cases students’ math achievement in sixth grade due to having an above average English teacher in fifth grade is almost as great as that due to having an equally above average math teacher in fifth grade. In contrast, while having an above average English teacher in fifth grade meaningfully affects students’ sixth grade English test performance, having a similarly above average math teacher in fifth grade has essentially no effect on English test performance. Data from New York City show that English teachers’ persistent effect on math is 70 percent of their persistence effect on English, while math teachers’ persistent effect on English is less than 5 percent of their persistent effect on math (see the following figure). Similarly, English teachers in Miami-Dade County Public Schools demonstrate a persistent effect on math that is 46 percent as large as their effect on English, while math teachers in the district have a persistent effect on English that is less than five percent as large as their persistent effect on math.
English teachers affect later student success across fields, while math teachers appear to only affect math performance. This pattern holds in both states studied, states with quite different state tests.
Why might the effects of good English teachers spill over into math learning, while the effects of good math teachers do not? One possibility is that the English curriculum might build capacities that are relevant for math learning. Reading skills and other linguistic skills, for example, might be key to understanding word problems on math exams. Similarly, English language arts teachers might promote the ability to think logically and organize complex materials, which, in turn, benefits math performance. An alternative explanation is that English teachers are able to motivate students, perhaps through drawing connections between the books they read and students’ experiences, in ways that math teachers do not. A study using data on ninth grade students in North Carolina schools found that teachers can affect students in ways not reflected by test scores, such as whether they come to school (attendance) or complete the work necessary to progress to the next grade. Teachers who are good at improving these non-test-based outcomes for students also positively affect their students longer run outcomes such as graduation and college and career aspirations.  That study shows that accounting for these effects that teachers can have on students is key to understanding English teacher effectiveness on students’ long-run outcomes, but far less important for understand math teachers’ effects. That is, good English teachers—those with the greatest long-run effect on students—affect not only test performance in English but also behaviors such as skipping school.
The large research base on teachers’ value-added to student test performance has consistently found that which math teacher a student has matters a lot for their learning during the year in that math teacher’s class and that the learning sticks with students in subsequent years. The findings for the importance of English teachers on English test performance have been clear but less strong. However, the research linking teachers to students long-run outcomes has found that English teachers are as important as math teachers. We are beginning to see the reasons for this. English teachers have important effects that go far beyond test performance and affect not only behaviors such as attendance and successful course completion but also test performance in other subject areas such as math.
Although the focus here is on teachers’ contributions to student learning, the findings may also have broader implications for other interventions that aim to develop students’ skills in reading and language arts. The results suggest that observed gains on English language arts assessments in the year of instruction do not fully capture the benefits that students are accruing from high quality English language arts instruction. The capacities that students are developing in their English classes—whether these be skills in logic or organization or the motivation they need to excel in school—are advancing their math learning almost as much as their learning in math class. Understanding what good English teachers are doing well may be just what we need to improve math outcomes for students.
— Suzanna Loeb
Susanna Loeb is the Barnett Family Professor of Education at Stanford University, faculty director of CEPA Labs, and a co-director of Policy Analysis for California Education.
This post originally appeared as part of Evidence Speaks, a weekly series of reports and notes by a standing panel of researchers under the editorship of Russ Whitehurst.
The author(s) were not paid by any entity outside of Brookings to write this particular article and did not receive financial support from or serve in a leadership position with any entity whose political or financial interests could be affected by this article.
1. THE MIRAGE Confronting the Hard Truth About Our Quest for Teacher Development. https://tntp.org/assets/documents/TNTP-Mirage_2015.pdf
6. See Rothstein, Jesse. 2010. “Teacher Quality in Educational Production: Tracking, Decay, and Student Achievement.” Quarterly Journal of Economics, 125(1): 175–214. And Kane, Thomas J., Jonah E. Rockoff, and Douglas O. Staiger. 2008. “What Does Certification Tell Us About Teacher Effectiveness? Evidence from New York City.” Economics of Education Review, 27(6): 615–31.
7. Master, B., Loeb, S., & Wyckoff, J. (forthcoming). “More than Content: The Persistent Cross-Subject Effects of English Language Arts Teachers’ Instruction,” Education Evaluation and Policy Analysis.