Laura Danly remembers that when she was in high school in suburban Chicago, she was one of two girls interested in science out of a class of more than 1,000 students.
"More than anything, I felt like I was 'one of the guys,' " said Dr. Danly, now a 33-year-old postdoctoral fellow at the Space Telescope Science Institute on the Johns Hopkins University campus.
"You spend your time at that age looking for approval from your teachers and your peers and they were all male. It's really only in the past year or two that I've persuaded myself that it's OK to be a woman and a scientist."
Dr. Danly's experiences are not unique. According to a report issued last week by the American Association of University Women, girls still lag behind boys in mathematics and science test scores and, perhaps more significantly, even those who do well on such tests do not tend to choose professions in those areas.
To try to make it easier on girls following her professional path, Dr. Danly has put together a series of monthly lectures and seminars on scientific topics for high school juniors and seniors with one distinction -- no boys allowed.
"I'm just trying to provide them with the type of experience I wish I had at their age," Dr. Danly said.
A variety of such programs over the years have helped Maryland become one of the nation's leaders in its percentage of female and male students choosing so-called non-traditional lines of study, said Marie Mayor, coordinator of interdisciplinary programs for the Maryland Board of Education.
"That's defined as any field in which less than 25 percent of the students are from one gender," she said. "So it might be boys in home economics or business courses, or girls taking welding or physics. Along with our educational programs to sensitize teachers to these needs, we find that mentoring programs are some of the most effective."
But Pnina Abir-Am, a visiting professor of the history of science at Hopkins, said mentors are not always enough.
"Students need role models," she said. Dr. Abir-Am has studied women in science and mathematics in the 19th and 20 centuries and finds that the pioneer women in these fields usually had two similar factors in their lives -- a helpful male mentor and a situation that allowed them to blend their familial and professional lives.
"It has been accepted through the years that men can put their family life on a lower rung, but not women," she said.
"That is to say nothing against women who decide to remain single or childless, but unless we show girls that it is possible to do both, many of them will not choose these professions because they do want to have families," said Dr. Abir-Am, who has consciously decorated her office with artwork by her 5-year-old daughter, Estee.
The cultural pressures that keep women out of science can be changed by policy-makers, pointing to the fact that when women were encouraged to become scientists in Eastern Europe and the former Soviet Union, their numbers rose to the expected proportions, Dr. Abir-Am said.
She emphasized that it would be in the United States' interest to adopt such policies, since "these days, to fill out its scientific work force, this country has to import foreign males while virtually ignoring this part of the population."
Her research has shown that the types of problems female scientists encountered historically would be familiar today -- namely day-care difficulties.
When pioneering mathematician Sofia Kovalevskaia took a faculty position in Stockholm, Sweden, in 1890, she left her children behind in a commune. "A century later, in 1990, I was invited to a two-week conference in Stockholm, and they were unable to provide child-care arrangements," Dr. Abir-Am said. "So, I could only go for one week."
Ms. Mayor remembered that when she scored in the top percentiles on a chemistry achievement test in high school, "my teacher encouraged me to study home economics because I would be allowed to take the same chemistry courses as the pre-med students.
"I did end up studying home economics, and it led me into this field where I've tried to work to break down the types of barriers that I faced."
Dr. Amir-Am said the situation was different when she went to college in Israel. "I chose to study chemistry in Israel, because it was 50-50 male-female and I thought it would be a place to have a normal social life.
"But at a recent meeting of the American Chemical Society, the statistics showed that only 11 percent of American chemists are women. Any minority that has less than 15 percent representation will feel uncomfortable in the situation," she said.
"For instance, if they say anything, people will not respond to what they have to say, but only to the oddity of their presence."