Sexism in the classroom teaches boys to be aggressive and girls to be subservient, reports a husband-and-wife research team that looked at more than 100 fourth-, sixth- and eighth-grade classes.

"Boys are allowed to talk out in class," says David Sadker of American University. "Girls are not."

That difference, say Sadker and his wife, Myra Sadker, exemplifies a pattern in which teachers, unless specially trained, give more encouragement, more attention and more challenges to boys.

They found that boys take up an average of 60 percent of classroom discussion time.

Writing in Psychology Today, the Sadkers cite this "typical" classroom scene as evidence of how boys are favored:

Teacher: "What's the capital of Maryland? Joel?"

Joel: "Baltimore."

Teacher: "What is the largest city in Maryland, Joel?"

Joel: "Baltimore."

Teacher: "That's good. But Baltimore isn't the capital. The capital is also the location of the U.S. Naval Academy. Joel, do you want to try again?"

Joel: "Annapolis."

Teacher: "Excellent. Anne, what's the capital of Maine?"

Anne: "Portland."

Teacher: "Judy, do you want to try?"

Judy: "Augusta."

Teacher: "Okay."

"It's not that teachers are more biased than everyone else," says Myra Sadker. "They're just like everyone else."

The researchers studied classrooms in the District, Maryland, Virginia, Massachusetts and Connecticut. With three days of training, she says, most teachers can overcome their bias.

But without it, they may be "looking at boys, seeing future achievers and investing their time there."