As students have returned to school, they have been greeted by teachers who, more likely than not, are white women. That means many students will be continuing to see teachers who are a different gender than they are and a different skin color.

Does it matter? Yes, according to a significant body of research: Students, especially nonwhite students, tend to benefit from having teachers who look like them.

The homogeneity of teachers is probably one of the contributors, the research suggests, to the stubborn gender and race gaps in student achievement: Overall, girls outperform boys, and white students outperform those who are black and Hispanic.

Yet the teacher workforce is becoming more female: 77 percent of teachers in public and private elementary and high schools are women, up from 71 percent three decades ago. The teaching force has grown more racially diverse in that period, but it is still 80 percent white, down from 87 percent.

There are many things that contribute to children’s academic achievement, including teachers’ experience and training; school funding and zoning; and families’ incomes and home environment. And teachers have long been predominantly white and female. But new educational opportunities for girls could mean that they can take more advantage of the benefits of female teachers. And studies show that teacher diversity can make a difference in students’ performance and their interest in school.

The effect is stronger on boys. Research has found that boys, and particularly black boys, are more affected than girls by disadvantages like poverty and racism, and by positive influences like high-quality schools and role models. Yet they are least likely to have had a teacher that looks like them.

“We find that the effect is really driven by boys,” said Seth Gershenson, an economist studying education policy at American University. “In the elementary school setting, for black children and especially disadvantaged black children, the effect of having even just one black teacher is fairly big and robust and a real thing.”

When black children had a black teacher between third and fifth grades, boys were significantly less likely to later drop out of high school, and both boys and girls were more likely to attend college, Gershenson and his colleagues found in a large study last year. The effect was strongest for children from low-income families. The study included 106,000 students who entered third grade in North Carolina from 2001 to 2005, and it followed them through high school. There was no effect on white children when they had a black teacher.

Teachers’ gender does not necessarily have a big effect during elementary school but seems to make more of a difference when children are older. Then, girls do better with a female teacher and boys with a male one, said Thomas Dee, a professor of education at Stanford.

When eighth-graders had a female teacher instead of a male one, boys fell behind girls by the equivalent of 3 1/2 months of learning, according to a well-regarded study he wrote, which compared the effect of two teachers of different genders on the same students. When students and teachers were the same gender, teachers also had more positive impressions of students, and students looked forward more to the subject. The study used Department of Education data on 25,000 eighth-graders from 1,000 schools.

In high school and college math and science courses, studies have shown that when women have a female instructor, they get higher grades, participate more in class and are more likely to continue to pursue the subject.

Researchers say it is not entirely clear why teachers’ gender and race make a difference; it is likely to be a combination of things. Students tend to be inspired by role models they can relate to. Same-race teachers might be able to present new material in a more culturally relevant way. Also, teachers sometimes treat students differently based on their own backgrounds and stereotypes. Social scientists call this implicit bias, when stereotypes influence people’s thinking, often unconsciously.

A variety of research, for instance, has shown that teachers tend to assess black students differently from white students. Preschool teachers judge black children more harshly for the same behavior. White teachers are less likely than black teachers to assign black students to gifted and talented programs even if their test scores match those of white students. When black students had both a white and black teacher, the black teachers consistently had higher expectations for the children’s potential.

Teachers’ biases can end up becoming self-fulfilling prophecy, Gershenson has found. “The high expectations actually motivate kids to do better,” he said. “Black students are hurt by that lack of optimism that white kids get, and black kids with black teachers rise to meet their expectations.”

Sometimes teachers underestimate students of their race or gender, suggesting that they have internalized stereotypes about their own group and that white and Asian-American students may not experience negative effects from having nonwhite teachers.

Girls perform about the same as boys in math on average through eighth grade. By age 17, there is a meaningful male advantage in that subject.

A new study, not yet published, found that math teachers favored boys over girls, and white students over black or Hispanic students — and that female teachers were biased in favor of boys and that nonwhite teachers were the most biased in favor of white students.

“These results indicate that enduring cultural biases may have long residual effects on stigmatized groups,” said Yasemin Copur-Gencturk, one of the authors and an assistant professor of education at the University of Southern California.

For the long term, the evidence suggests it would make a difference to train and hire more diverse teachers. But researchers say there is something schools can do immediately, with the teachers they have: Teach them about their biases and stereotypes. It can lead to fairer treatment of students.

The research shows that no matter their demographics, teachers can overcome some of the effects of bias, Dee said. He summed up the interventions this way: “Signal to students your deep faith in their capacity to learn, coupled with your high expectations that they’ll do great things, full stop.”

It is surprisingly effective and simple to do, social scientists have shown. One study found that merely informing teachers about their stereotypes closed gaps in grading. An hourlong online tutorial for teachers has halved suspension rates for black students, after training educators on how to value students’ perspectives and view misbehavior as a learning opportunity.

Another strategy is coaching teachers on how their language can unintentionally signal to students that they cannot excel. Teachers are taught to convey to students that intelligence is not fixed, but built through hard work, and to talk about each student’s value and belonging in the classroom.

Retaining current teachers is also important, researchers say. More qualified people would stay in the field if the jobs had better pay, benefits and support. Nonwhite teachers in schools with poor resources are at particular risk of burning out.

“It also matters just to have a really good teacher,” Dee said. “We don’t want to lose sight of that as we support diversity.”

© 2018 The New York Times Company