My wife and I have sent five children to college and our youngest just graduated. Like many parents, we encouraged them to study hard and spend time in a country where people don't speak English. Like all parents, we worried about the kind of people they would grow up to be.

We may have been a little unusual in thinking it was the college's responsibility to worry about that too. But I believe that intellect and virtue are connected. They influence one another. Some say the intellect is primary. If we know what is good, we will pursue it. Aristotle suggests in the "Nicomachean Ethics" that the influence runs the other way. He says that if you want to listen intelligently to lectures on ethics you "must have been brought up in good habits." The goals we set for ourselves are brought into focus by our moral vision.

"Virtue," Aristotle concludes, "makes us aim at the right mark, and practical wisdom makes us take the right means." If he is right, then colleges and universities should concern themselves with virtue as well as intellect.

I want to mention two places where schools might direct that concern, and a slightly old-fashioned remedy that will improve the practice of virtue. The two most serious ethical challenges college students face are binge drinking and the culture of hooking up.

Alcohol-related accidents are the leading cause of death for young adults aged 17-24. Students who engage in binge drinking (about two in five) are 25 times more likely to do things like miss class, fall behind in school work, engage in unplanned sexual activity, and get in trouble with the law. They also cause trouble for other students, who are subjected to physical and sexual assault, suffer property damage and interrupted sleep, and end up babysitting problem drinkers.

Hooking up is getting to be as common as drinking. Sociologist W. Bradford Wilcox, who heads the National Marriage Project at the University of Virginia, says that in various studies, 40%-64% of college students report doing it.

The effects are not all fun. Rates of depression reach 20% for young women who have had two or more sexual partners in the last year, almost double the rate for women who have had none. Sexually active young men do more poorly than abstainers in their academic work. And as we have always admonished our own children, sex on these terms is destructive of love and marriage.

Here is one simple step colleges can take to reduce both binge drinking and hooking up: Go back to single-sex residences.

I know it's countercultural. More than 90% of college housing is now co-ed. But Christopher Kaczor at Loyola Marymount points to a surprising number of studies showing that students in co-ed dorms (41.5%) report weekly binge drinking more than twice as often as students in single-sex housing (17.6%). Similarly, students in co-ed housing are more likely (55.7%) than students in single-sex dorms (36.8%) to have had a sexual partner in the last year—and more than twice as likely to have had three or more.

The point about sex is no surprise. The point about drinking is. I would have thought that young women would have a civilizing influence on young men. Yet the causal arrow seems to run the other way. Young women are trying to keep up—and young men are encouraging them (maybe because it facilitates hooking up).

Next year all freshmen at The Catholic University of America will be assigned to single-sex residence halls. The year after, we will extend the change to the sophomore halls. It will take a few years to complete the transformation.

The change will probably cost more money. There are a few architectural adjustments. We won't be able to let the ratio of men and women we admit into the freshman class vary from year to year with the size and quality of the pools. But our students will be better off.

Mr. Garvey is president of The Catholic University of America in Washington, D.C.