The following short summary is an excerpt from the National Association for Single-Sex Public Education
Students at All-girls Schools Less Likely to Get Pregnant
Middle and high school girls who attend single-sex schools are less likely to get pregnant than their co-ed counterparts. However, the reason is not as obvious as you may think.
Surprising research by Professors Katherine Sanders and Neville Bruce at the University of Western Australia found that students at all-girls schools have just as many heterosexual relationships as the co-ed girls, but they are under less pressure to have sex with their boyfriends.
A co-ed environment creates an atmosphere that puts girls under pressure to have sex at earlier ages, the researchers found. Students at co-ed schools form cliques made up of both boys and girls. Girls are more likely to choose boyfriends from within their cliques rather than because they prefer certain boys as individuals. If all the other girls in their clique are having sex with their boyfriends, that puts more pressure on a girl to conform and engage in it too. Saying no not only jeopardizes a girl's relationship with her boyfriend, but also with her entire circle of friends.
At single sex schools, girls keep their romantic heterosexual relationships separate from their friendships at school. Drs. Bruce and Sanders found that girls at all-girls schools found it easier to say no to sex because they still had a social life if they lost their boyfriends.
Teenage pregnancy is a top concern in the United States, which has the highest rate of teen births in the industrialized world. Nearly forty percent of American young women become pregnant before they are twenty years old. More than eighty percent of those pregnancies are unplanned.