Higher-quality teachers not only can help students boost their test scores, but also help students have better long-term outcomes, a study says.

"The Long-Term Impact of Teachers: Teacher Value-Added and Student Outcomes in Adulthood," a study by professors Raj Chetty and John N. Friedman of Harvard University and Jonah E. Rockoff of Columbia University, looked at more than 2.5 million students and 18 million math and English tests from 1989 to 2009. The study sought to assess the effect that a teacher with high "value-added" (VA) ratings has on student performance.

A teacher’s VA is defined as the average test-score gain for his or her students, adjusted for differences across classrooms in student characteristics such as prior scores.

"We find that students assigned to higher VA teachers are more successful in many dimensions," the researchers conclude. "They are more likely to attend college, earn higher salaries, live in better neighborhoods, and save more for retirement. They are also less likely to have children as teenagers."

The study says that replacing a teacher whose true VA is in the bottom 5 percent with a teacher of average quality would generate lifetime earnings gains worth more than $250,000 for the average classroom.