Gender stereotypes may be turning girls off careers in maths and science, according to an international study.
It suggests that parents are more likely to encourage their sons to pursue these subjects.
The report, by the Organisation for Economic Co-operation and Development (OECD) examined the different gender gaps in education.
It found that while many countries have made significant progress in closing the gap in many areas, there are new ones opening up, with young men much more likely to have low levels of skills and academic achievement, which makes them more likely to leave school early.
Internationally, six in 10 low achievers in international reading, maths and science survey are boys, the OECD says.
At the same time, women are much less likely to study many science and maths-based subjects and to have the same self-confidence as boys in these areas.
Across the 64 nations examined, less than one in 20 girls considers a career in science, technology, engineering and maths (Stem), compared to one in five boys, despite the sexes achieving similar results in international science tests.
Parents, teachers and employers may all have "biases" that fuel gender gaps, the report suggests.
In many countries, mothers and fathers are more likely to expect their sons to work in Stem industries than their daughters, even if they have similar abilities in these subjects, it notes.
Teachers generally award girls higher marks than boys, given what would be expected given their performance in international tests.
"Girls' better marks may reflect the fact that they tend to be 'better students' than boys: they tend to do what is required and expected of them, thanks to better self-regulation skills, and they are more driven to excel in school," it says.
But this may disadvantage girls, the OECD suggests, as employers tend to reward people based on what they know and can do rather than their school grades.
The OECD also argues that employers may tend to favour boys because they are more likely than girls to get hands-on experience working as interns, visiting job fairs or speaking to careers advisers outside of school.
"Parents can give their sons and daughters equal support and encouragement for all of their school work and aspirations for their future. PISA results show that this doesn't always happen," the report says.
"In all countries and economies that surveyed the parents of students who sat the Pisa test, parents were more likely to expect their sons, rather than their daughters, to work in a science, technology, engineering or mathematics field - even when their 15-year-old boys and girls perform at the same level in mathematics.
"Teachers can help by becoming more aware of their own gender biases that may affect how they award marks to students. They could also receive additional training in how to provide extra support to socio-economically disadvantaged students, since Pisa finds that boys are more likely to underachieve when they attend schools with a large proportion of disadvantaged students."
The study also argues that teachers and parents should give children more choice in what they read, and encourage boys to read comics, newspapers or magazines to foster their enjoyment of reading. This would help to improve reading skills.
In a foreword to the report, OECD secretary-general Angel Gurria, said: "Gender disparities in performance do not stem from innate differences in aptitude, but rather from students' attitudes towards learning and their behaviour in school, from how they choose to spend their leisure time, and from the confidence they have - or do not have - in their own abilities as students.
"In fact, the report shows that the gender gap in literacy proficiency narrows considerably - and even disappears in some countries - among young men and women in their late teens and 20s.
"Giving boys and girls an equal opportunity to realise their potential demands the involvement of parents, who can encourage their sons and daughters to read; teachers, who can encourage more independent problem solving among their students; and students themselves, who can spend a few more of their after-school hours 'unplugged'."
Michael Reiss, professor of science education at the Institute of Education, said: "We are one of the countries with the biggest gender differences in the OECD PISA science results. Our 15-year-old girls are reported as doing 13% less well than our boys. Of the 67 countries that took the tests, this places us in the bottom five.
"The findings are hard to believe and don't agree with the annual GCSE results in England, Wales and Northern Ireland and the equivalent examinations in Scotland. However, if these findings are valid, they are deeply disturbing.
"We know that students who do less well in science are less likely to continue with it and we know that students who take science degrees end up glad that they did and get well paid jobs.
"So what might be going on? This is nothing to do with genetics. Across the 67 countries that took the tests, the average gender difference in science was only 1%. The explanation must be a cultural one.
"Despite television presenters like Alice Roberts and the increasing prevalence of senior female scientists in the UK (Dame Athene Donald, Dame Julia Goodfellow, Dame Julia Higgins, Dame Julia King, to mention just four), what girls too often seem to be hearing is that science is not for them."
A Department for Education spokesman said: "Our plan for education is ensuring all pupils develop the skills and knowledge which give them the best possible chance to succeed.
"A key part of this is our focus on crucial STEM subjects like science and maths - we are attracting top STEM graduates into teaching and plan to invest £67m in this area over the next five years.
"We are also supporting the Your Life campaign to show young people - and especially girls - the exciting opportunities these subjects can bring."