FOR BOYS ONLY: Linwood College pupils Shayne Hume and Jerome Davis take part in a boys-only science class, aimed at boosting their achievement.

New Zealand boys are further behind girls in the classroom than in any other developed country, and the head of a Christchurch boys' school blames marital splits.

The 30-member Organisation for Economic Co-operation and Development (OECD) yesterday released a report comparing achievement by 15-year-old boys and girls in 40 countries.

Of the OECD countries in the study, the difference in reading achievement in favour of girls was greatest in New Zealand, the report showed.

"There are significant gender differences in educational outcomes, and these appear as students grow older."

Last year's National Certificate of Educational Achievement (NCEA) results, released this month, showed girls outperforming boys by wider margins as pupils got older.

"It's an issue that boys' schools have an opportunity to address," St Bede's College rector Justin Boyle said.

Boys seemed to have particular difficulty with writing, and the school had introduced a programme to improve writing skills, he said.

"I believe also there are other social issues; who are the male role models who are influencing these boys?" Boyle said.

"Invariably, we find if mum and dad have split they have not had the male role model in their lives to encourage them in a holistic way about how they get educated."

Divorce statistics released this month showed about one-third of New Zealanders who married in 1983 had divorced before their 25th wedding anniversary.

Education consultant Joseph Driessen said children who came from broken homes were typically 25 per cent behind other children in achievement.

"Boys are affected by divorce very deeply because 85 per cent of custody goes to the mother and guys just disappear. That needs to change," he said.

"We need to have a family split-up philosophy where we realise that sons need their fathers. All custody and access should be 50-50."

Boyle said boys' schools could help form well-rounded men. "We are in a good position in a boys' school to look at particularly boys' issues and address them head-on," he said.

The OECD report said single-sex schools in New Zealand were more effective for girls than for boys.

Co-educational Linwood College runs two boys-only classes for struggling boys.

"They do exactly the same curriculum as any other student. It's the context and the topics that might change," principal Rob Burrough said.

He said NCEA assessment was better suited to girls.

"Schooling does tend to favour girls and the way they learn. Internal assessment is more user-friendly for many girls," he said.

"Academic achievement is just one measure of intelligence, so it's a matter of adapting to success in today's education environment, and teachers have to provide a variety of teaching experiences to cater for different learning styles."

A Ministry of Education report released yesterday showed boys outnumbered girls by more than two to one in needing specialist literacy teacher help.