Girls and boys in Wales are still choosing "traditionally" female and male subjects at GCSE and A-level, and the gender gap is particularly stark in vocational qualifications, according to a TES Cymru analysis.
It has led to warnings that more needs to be done to ensure that plans to widen vocational choices for 14 to 19-year-olds do not lead to an even bigger gender gap.
Young women are already missing out on better-paid jobs because of poor advice and subject choice, according to the Equal Opportunities Commission Wales.
Its own analysis found that only one in 10 girls studied engineering at age 18 - a sector paying trainees pound;167 per week, compared with pound;95 a week for nursery-nurse trainees.
The Assembly government's learning pathways reforms envisage a wider choice of vocational and work-based courses for 14 to 19-year-olds, aimed at reducing drop-out rates and improving qualifications.
But a TES analysis of last summer's exam entries shows vocational GCSE subjects were the most starkly divided along gender lines. Health and social care, the subject with the largest number of entries (2,470), was dominated by girls (95 per cent).
Manufacturing and engineering together accounted for around 1,100 entries, almost all from boys. They also outnumbered girls by almost two to one on vocational GCSE IT courses.
Entries were balanced for vocational science GCSE. A spokeswoman for the WJEC, the Welsh exam board, said that this was largely because the subject is compulsory up to age 16 rather than because the syllabus is more "girl-friendly".
Brian Rowlands, secretary of the Association of School and College Leaders Cymru, said the figures were a cause for concern.
"With impending curriculum reforms at 14-19, and the encouragement of vocational subjects in particular, it's important this gender gap is closed rapidly," he said.
"Correct course advice is essential. The new 14-19 learning coaches have an important role to play."
Anna Brychan, director of the National Association of Head Teachers Cymru, said officials should look to other countries' examples to address the problem.
She added: "We would hate to see this strict gender separation continue as options for vocational training at 14-19 are extended, especially with its implications for future earning capacity."
An Assembly spokesman said the learning pathways action plan sets out a timetable for ensuring equal opportunities. These include working with employers to stop stereotyping, and providing training materials.
He added: "We want to encourage young people to pursue the options which best suit their aptitudes, from a wide choice. High-quality careers advice is one key."
The analysis shows pupils are also divided along traditional gender lines at A-level, with little change since 2001. Girls accounted for 57 per cent of entries in biology and 60 per cent or more in English, art, foreign languages and RE. Males outnumbered females by a similar proportion in design and technology, ICT, physics, maths and PE.