When Liz O'Day entered the honors chemistry program at Boston College with about 40 students her freshman year, nearly half of her classmates were women. Two years later, she was one of only three who had not dropped out.
Then, to the dismay of the senior biochemistry major, O'Day found that many girls were losing interest in science much earlier. After speaking last spring to several Boston-area high schools about her research on developing a way to stop cancer cells from growing, O'Day said girls told her that they thought science was lame, boring, too hard, and just plain uncool.
''Everyone's imagining scientists as a bunch of dorks who can't be social and can't hang out," said O'Day, who also plays fullback for the Boston College women's rugby team.
''But science has revolutionized my life. I get to travel. I get paid to do what I love. I have a career now. I want to ensure that if someone has the potential to do well in science, that they're being encouraged."
So O'Day, a 22-year-old Braintree native, recruited 20 of her fellow women science majors at Boston College to help push more girls into science.
Each Saturday this month, the women teach a hand-picked group of 31 high school girls the wonders of science through a series of gee-whiz experiments and learning by example.
Yesterday, the college students worked with high school girls to turn a shiny copper penny a silver color, then gold, by oxidizing the coin.
Some analyzed two sequences of DNA in a forensics experiment to figure out which matched the crime scene. Others tried their hand at cloning a gene from malaria-transmitting mosquitoes.
Not all the girls in her Women in Science and Technology program are stellar science students, said O'Day, who said she accepted girls she felt the program could inspire the most. In addition to lab research, the girls listen to women scientists talk about their careers or take field trips to the Weston Observatory and Genzyme in Framingham
Mary Roberts, a Boston College chemistry professor who taught O'Day last year, said the shortage of women in science has improved since she started graduate school in 1969, when there were only two other women in her class.
''Those were the dark ages," Roberts said. ''But Liz sees there is still a problem, that girls in high school lose interest in science."
Like many of the girls in the program, Ashlee Sweeney, a senior at Braintree High, already has a strong interest in science and applied to the program because she wanted lab experience before college.
''Programs like this make me feel more confident that I can achieve higher goals," said Sweeney, who wants to major in biology in college and become a pediatrician. ''You also recognize that there are more girls who want to pursue science."
Kelli Thomas, a senior at Fontbonne Academy in Milton, said the program has even piqued the interest of her nonscience-inclined friends.
''The girls who kind of don't like science are wishing they did it, because they just hear me talking about it," said Thomas, who wants to major in forensics and criminal justice in college.
The second of three children, O'Day said she became interested in science in the first grade when her older brother, now 24, was diagnosed with neuroblastoma, a form of cancer.
The family spent two years at Children's Hospital in Boston while he went through chemotherapy and surgeries. She befriended other children with cancer, some of whom died.
She found science classes fascinating as she got older, because she liked figuring out how and why things work. She majored in biochemistry so she could invent drugs to treat illnesses such as cancer. After winning more than $30,000 in science fellowships, O'Day said she wanted to show younger girls that they, too, could succeed in science and have opportunities like hers.
She began planning her program last summer, enlisting support from women professors in chemistry and biology and e-mailing companies for donations, tours, and speakers. Various Boston College groups and a chemical company donated $3,500 for transportation, supplies and food.
Yesterday, O'Day cut short a trip to Yale University, where she has been accepted to the PhD program in biochemistry, so she could return to Boston in time to run the high school program. She plans to defer graduate school and spend next year abroad -- either pursuing a master's degree in chemistry at the University of Cambridge in England on a Winston Churchill Scholarship or researching protein folding in Bangalore, India on a Fulbright Fellowship.
O'Day said she hopes the younger Boston College students will continue the Women in Science and Technology program next year and expand the number of girls and schools served.
''It's fun to figure out what makes something work," said Chi Chi Egesionu, a junior at Trinity Catholic High School in Newton who wants to be a pharmacist like her father. ''I don't find science hard at all."