Are boys and girls really that different? Twenty years ago, doctors and researchers didn't think so. Back then, most experts believed that differences in how girls and boys behave are mainly due to differences in how they were treated by their parents, teachers, and friends.

It''s hard to cling to that belief today. An avalanche of research over the past twenty years has shown that sex differences are more significant and profound than anybody guessed. Sex differences are real, biologically programmed, and important to how children are raised, disciplined, and educated.

In Why Gender Matters, psychologist and family physician Dr. Leonard Sax leads parents through the mystifying world of gender differences by explaining the biologically different ways in which children think, feel, and act. He addresses a host of issues, including discipline, learning, risk taking, aggression, sex, and drugs, and shows how boys and girls react in predictable ways to different situations.

For example, girls are born with more sensitive hearing than boys, and those differences increase as kids grow up. So when a grown man speaks to a girl in what he thinks is a normal voice, she may hear it as yelling. Conversely, boys who appear to be inattentive in class may just be sitting too far away to hear the teacher-especially if the teacher is female.

Likewise, negative emotions are seated in an ancient structure of the brain called the amygdala. Girls develop an early connection between this area and the cerebral cortex, enabling them to talk about their feelings. In boys these links develop later. So if you ask a troubled adolescent boy to tell you what his feelings are, he often literally cannot say.

Dr. Sax offers fresh approaches to disciplining children, as well as gender-specific ways to help girls and boys avoid drugs and early sexual activity. He wants parents to understand and work with hardwired differences in children, but he also encourages them to push beyond gender-based stereotypes.

A leading proponent of single-sex education, Dr. Sax points out specific instances where keeping boys and girls separate in the classroom has yielded striking educational, social, and interpersonal benefits. Despite the view of many educators and experts on child-rearing that sex differences should be ignored or overcome, parents and teachers would do better to recognize, understand, and make use of the biological differences that make a girl a girl, and a boy a boy.