Two-thirds of bachelor degrees last year went to women, the highest figure on record in New Zealand.

Women have outnumbered men in the tertiary sector for more than a decade, but a new Ministry of Education report shows the number of men who finish bachelor degrees is falling.

Education experts warned that if the trend continued, it would have far-reaching social and economic consequences.

Reasons for the widening gender gap include an increase in men going into trades and a secondary school system which may discourage or poorly prepare boys for further learning.

Between 2006 and 2008 the number of male students completing a bachelor degree fell from 7600 to 6900.

In the same period the number of female students completing bachelor degrees increased by 100 to 12,900.

Director of the Institute of Policy Studies Dr Paul Callister said he was surprised by the latest figure. Tertiary organisations believed the gender gap had peaked.

"Universities have often argued that men were just falling behind relatively [to women]. But they are now falling behind in sheer numbers too.

"It wouldn't be a concern if males were pouring their way into other training options. But ... females are a higher proportion of all training options from Level 1 to 3 to doctorates."

Dr Callister emphasised that the creation of a high-income, high-employment society depended on getting more men into university, and then ensuring the completion of their degrees.

Boys' underachievement in education was a historical problem, rooted in a lack of ambition and poorer writing skills.

The gender gap began to develop as soon as boys entered school, but was most noticeable in NCEA Level 3.

Auckland Grammar headmaster John Morris said the NCEA curriculum had contributed to the gender gap, as the internal assessment system favoured girls. He said boys succeeded better in exam-based schooling.

Waitaki Boys High School rector Dr Paul Baker was a member of a ministerial review to guide the Government on boys' education.

He said the growing difference between male and female students' achievement at undergraduate level meant a significant proportion of the population was not reaching its potential.

"The tertiary gender gap has been growing at almost 1 per cent a year. If that carries on for another decade ... it will impact down the line ... on the composition of families, and the workplace."

A recent paper by the Equal Employment Opportunities Trust showed many traditionally male-dominated professions - medicine, law, accounting and planning - were now dominated by women at a junior level.

The paper by Dr Mervyl McPherson showed that if women continued to fill these roles at a greater rate than men, workplaces would have to adapt.

Women will reach a point where they can step into a management role, but will leave mid-career to have children, creating a hole in company structures that risks it losing vital knowledge.

Dr Baker said there was no simple solution the Ministry of Education could provide to close the gap, and felt there was a need for greater research on the topic in New Zealand schools.

He said there was some promise in the new national standards curriculum, because it focused on how to teach, instead of what is taught.

"It is quite boy-friendly. Boys need really good teaching while girls are more likely to do reasonably well regardless of the quality of the teacher."

Dr Callister said the new curriculum will give some hard data, from the first year of school, on where boys are going wrong.

"But then we've got the harder part of how to fix it."

Out of all students completing bachelor degrees in 2008, 65 per cent were female - 3 per cent more than in 2001.