Some people questioned why Mr. Ratnayake, who has degrees in aerospace engineering and six years' experience studying issues like supersonic propulsion for NASA, was moving from a testosterone-fueled field to one overwhelmingly inhabited by women. He's now enrolled in the Boston Teacher Residency program, which offers a master's degree in education from the University of Massachusetts at Boston.
But as the son of immigrants from Sri Lanka and the grandson of four teachers, he was able to look beyond the gender stereotypes. He hopes the students he will teach will do the same.
"I'd like to think that I could be a role model for males wanting to become teachers, as well as females considering physics or engineering," says Mr. Ratnayake. "Every field," he says, "whether it's engineering or teaching or politics or art, benefits from having a diverse array of perspectives."
Engineering and teaching are among the most lopsided disciplines in academe's gender split. In 2010, women received 80 percent of the undergraduate degrees awarded in education, the U.S. Education Department reports. And they earned 77 percent of the master's and 67 percent of the doctoral degrees in that field.
In engineering, by contrast, women earned just 18 percent of undergraduate, 22 percent of master's, and 23 percent of doctoral degrees.
Nationally, women are heading to college in record numbers and now make up 57 percent of undergraduates. Women also earn 60 percent of all master's and 52 percent of all doctoral degrees, according to U.S. Education Department statistics, which include doctorates earned in professional fields like medicine and dentistry. But for all the efforts colleges are making to diversify their departments, some fields of study remain stubbornly single sex.
At the undergraduate level, some of the most female-intensive disciplines are in health professions and related clinical sciences, where women make up 85 percent of the majors; in psychology, where 77 percent of majors are women; and in English and foreign languages, with 68 and 69 percent women.
Among the more male-dominated fields for undergraduate majors are philosophy and religious studies, at 63 percent (see related article on facing page), and mathematics, at 57 percent.
Perhaps nowhere has the gender gap been more pronounced, or more studied, than in science, technology, engineering, and mathematics—the STEM fields. Women are still a minority in those fields despite more than a decade of outreach.
Researchers at Rice University found, in a study released this month, that both male and female scientists view gender discrimination as a factor in women's decisions not to pursue a science career or to opt for biology over physics.
Not surprisingly, the gender distribution of professors in the STEM disciplines is similarly skewed.
Kristen Renwick Monroe, a professor of political science at the University of California at Irvine, is spending the year at Harvard University's Radcliffe Institute for Advanced Study writing a book about gender equality in academe. Her continuing surveys confirm one commonly acknowledged struggle that many women face in climbing the career ladder: Integrating work and personal lives can be difficult since women still tend to bear the primary responsibility for housework, as well as for the care of children and elderly parents.
"A critical problem in sciences or in any profession where you have to be in the office all day is that it's hard to have that job and raise children," Ms. Monroe says. "My job as a political-science professor is much more flexible. I can teach courses while my kids are in school, stay up late, or sit at the computer and work while my daughter reads at the table near me. I couldn't do that if I were a doctor having to see patients or a research scientist responsible for a lab."
But no matter how many hours a woman puts into the job or how well qualified she is, "there's still a lot of implicit prejudice," says Ms. Monroe. In hiring and promoting, department administrators often assume that a woman with children is very likely to be distracted by outside demands. "They don't always think about that with men."
Political science is typical of many disciplines in which the percentage of women shrinks as they move from assistant to full professor. "The pipeline leaks women more than it leaks men," she says.
Donna J. Nelson, a professor of chemistry at the University of Oklahoma, has studied the participation of women and minorities in tenured and tenure-track positions in science and engineering departments at the top-100 research universities.
She found that, over the last 10 years, sociology and political science had the largest gains for women, while electrical engineering had the smallest increases. And while many researchers have focused on the difficulties of juggling kids and careers, she believes that the problems that make some environments unwelcoming to women are broader than that. "Simply putting day-care centers into every place isn't going to solve all the problems facing women," she says.
For one thing, women's input isn't always valued as highly as men's when it comes to important matters, she says. In her own case, that meant being appointed to a library committee when she had asked to serve on one that dealt with larger budget issues.
Students can also be swayed by cultural stereotypes, and the results show up across campuses. Many still view science and math as male fields and humanities and art as female, the American Association of University Women pointed out in a 2010 report. The report noted that boys and men tend to score higher in spatial skills that are important in fields like engineering, but with the right support and exposure, girls can be just as successful.
The problem is, they often don't get that encouragement. There are fewer role models and mentors in traditionally male fields, and even academics who profess to support women often harbor hidden biases. A recent study by researchers at Yale University found that science professors at American universities often viewed female undergraduates as less competent than their equally-qualified male peers. Surprisingly, female professors were just as likely to favor a male candidate for a position as lab manager when they were given identical applications with either male or female names. The male student was also offered a higher starting salary and more mentoring.
A similar study by researchers at the University of Pennsylvania's Wharton School found that professors in a variety of disciplines were much less likely to be responsive to communication from women or minority applicants to doctoral programs, and that the problem was worse in academic disciplines that tend to pay more.
Lawrence H. Summers, the former president of Harvard University, famously suggested in 2005 that innate differences in ability between men and women might partly explain why fewer women excel in mathematics and science. Critics accused him of reinforcing a stereotype, but his remarks also opened a discussion about the roles that both society and biology might or might not play in the choices women make and the options available to them.
In the professional schools, female students have basically achieved parity in law and medicine. In M.B.A. programs, however, they still represent only 36 percent of enrolled students in the United States—virtually unchanged from 10 years ago.
Some women who are eager to start careers before they have children are more attracted to graduate programs like law and medicine that they can join right after college graduation. Top M.B.A. programs usually require applicants to work for three to five years before entering a two-year program. Business schools have, in recent years, expanded specialized, one-year master's programs, often open to students with less work experience, that have proven particularly popular with women.
For schools of education, the problem is attracting men.
Even though economic downturns have tended, in the past, to drive more men into teaching, it's not clear that that's happening today. Low teacher salaries are the most common explanation for gender imbalance. But researchers at a conference of the American Educational Research Association suggested that men might also be discouraged by the diminishing status of teachers and the suspicion that many people have about the motives of men working with children.
"The stereotypes are pushing men away," says Bryan G. Nelson, founding director of MenTeach, a nonprofit group that is trying to attract more men to the profession.
Mr. Ratnayake, the Boston teaching resident, recently wrote about his career transition on the MenTeach Web site. When a friend warned him that the move could doom his dating life by raising doubts about his masculinity, he laughed it off.
"I guess I wasn't aware that science nerds and engineers were a particularly hot commodity, though to be fair, I don't think I actually ever tried the 'Hey baby, I'm a rocket scientist' line at a bar," he wrote. "The times I could have had. ... "