For centuries the most elite college and universities in the United States and the United Kingdom were single-sex. Then, in the period 1969-74, there was a flood of decisions for coeducation on both sides of the Atlantic.

Why did so many very traditional, conservative, elite colleges and universities decide to embark on such a fundamental change? Why then? How did the decisions get made? How was coeducation accomplished in the face of strong opposition? And what happened? How well did coeducation work in its early incarnations? Those are the questions that frame my new book, “Keep the Damned Women Out”: The Struggle for Coeducation.

As for why, coeducation happened because it was in the strategic self-interest of all-male institutions like Princeton and Yale (and later Dartmouth) to admit women. By the late 1960s, these schools were beginning to see their applications decline, along with their yields. The high school students they called the “best boys” no longer wanted to go to all-male institutions. The key issue was the ability to continue to attract those “best boys.” Coeducation became the means to shore up a first-rate applicant pool and enrolled student body.

Coeducation was not the result of a high-minded moral commitment to opening educational opportunities to women. It was not a matter of a mission to educate women. It was not the result of deep thinking about how to educate women. Rather, it was about what women could do for previously all-male institutions—how women would help these schools renew their hold on the “best boys.” Women played the instrumental role of improving the educational experience of men. It is not surprising that going coed did not always well serve the women who were admitted to the early coed classes.

A related point: The protagonists in this story are men. Save for Radcliffe president Mary Ingraham Bunting, every strategist, every decision-maker, everyone leading the charge for coeducation was male. Coeducation resulted not from organized efforts by women activists but from strategic decisions taken by powerful men.

Why did coeducation happen when it did? Everything about the 1960s helps to answer that question. The civil rights movement, the antiwar movement, the student movement, the women’s movement—by the end of the 1960s, colleges and universities looked quite different than they had at the beginning of the decade. Student bodies began to include a large number of public school students as well as students from less advantaged families, Catholics and Jews, even African Americans. Coeducation followed logically. Men and women students demonstrated together, protested together, registered black voters together. Not going to school together seemed increasingly outmoded. Not surprisingly, high school students changed their minds about the attractiveness of single-sex schools.

What factors affected the implementation of coeducation? The first was leadership. The more skillful the president, the easier it was to imagine, and then move the institution to embrace, a different future. Presidents needed to convince trustees, deal with alumni, and mobilize internal planning and execution to make coeducation happen. The less effective the leader, the easier it was for the many forces of opposition to throw sand in the gears.

The second point has to do with process. The more an institution invested in careful analysis and planning, the more likely it was to contain the opposition and introduce coeducation reasonably smoothly. In the absence of adequate process, newcomers—especially women—had a more difficult time.

Making these changes happen was extremely difficult. There was significant resistance from many faculty and students as well as alumni. Some examples illustrate the point.

As for alumni, consider the title of my book. It comes from a 1970 letter from a Dartmouth alumnus to the chair of the Dartmouth trustees: “For God’s sake, for Dartmouth’s sake, and for everyone’s sake, keep the damned women out.”

Or some examples from Princeton alumni: “Why this death wish on the part of Princeton?” If women were admitted, “Princeton University would be lost forever.” Coeducation would dilute “Princeton’s sturdy masculinity with disconcerting, mini-skirted young things cavorting on its playing fields.” And, “What is all this nonsense about admitting women to Princeton? A good old-fashioned whore-house would be considerably more efficient, and much, much cheaper.”

As for faculty, some were supportive, some were opposed, but virtually everyone put the newly admitted women students on the spot by asking for “the woman’s point of view,” no matter whether the course was in literature or psychology, where such a view might have been relevant, or in math or physics, where it wasn’t. As for explicit insults, consider the art history professor at Dartmouth who posted slides of nudes on the screen, running his hand up and down their thighs, or the oceanography professor who showed pictures of shrimp and lobster, squid, and naked women. Or the Yale history department chair, asked about offering a course in women’s history, who responded that that would be like teaching the history of dogs.

As well, there were regular outbursts from male students unaccustomed to having women in their classes. The benign version: “It’s a girl! It talks!” Dartmouth men hung banners from dormitory windows: “No Coeds”; “Coeds Go Home.” They shouted out numbers meant as ratings of attractiveness as women entered the dining hall. Fraternities delighted in drunken, dangerous behaviors, aggressive sexual encounters, and scurrilous verbal assaults on women students. In the third year of coeducation, the winning entry in the annual intra-fraternity Hums competition was the song “Our Cohogs,” ten verses of insulting, sexualized attacks on women. (“Cohog” was a highly derogatory nickname for women students.) The judge of the competition, the dean of the college, chose “Our Cohogs” as the most original submission and joined fraternity members in an exuberant public rendition of the song.

But after a somewhat rocky start, involving only a small number of women students, coeducation prevailed. Women took their rightful place, excelled academically, and began to assume leadership roles. Women now represent half the student body, and coeducation is the accepted norm. Today’s students find it unimaginable that going coed was ever considered revolutionary.