New Zealand's infant mortality rate - babies who die before their first birthdays - has fallen steadily from 25 for every 1000 births in the early 1950s to 4.8 for every 1000 in the Unicef data, and to 4.2 in the latest Statistics NZ figures for 2012.

But New Zealand's rate is still higher than most other developed countries apart from the United States.

Nelson paediatrician Dr Nick Baker, who chairs the child and youth mortality review committee, said New Zealand's high rate was largely due to sudden infant death syndrome and specifically babies suffocating while sleeping in unsafe positions such as with parents or siblings.

"Adult beds have lots of places where babies can get trapped, making it hard to breathe," he said.

"Even in cots, we still have ill-fitting mattresses or cot sizes where a baby can get trapped."

He said 60 Kiwi babies died of SUDI every year and if we could reduce the SUDI rate to that of the Netherlands, only 12 would die. New Zealand's "NEET" rate, compared with international rates for the first time in this survey, is the biggest shock in the figures - worse than all other developed nations except Spain and Bulgaria.

The figure, 12 per cent of those aged 15 to 19 not in employment, education or training, dates from the 2009-10 peak of youth unemployment. Statistics NZ says the rate has fallen since then to 9.6 per cent by the end of last year.

But Business NZ chief executive Phil O'Reilly said the present school system was clearly not working for too many young people.

"We have this long tail of under-achievement, and it's a long, brown tail dominated by young Maori and Pacific kids," he said.

Council of Trade Unions secretary Peter Conway said young people were affected by shrinking numbers in industry training and in wananga, while new initiatives such as trade academies and "vocational pathways" in schools were slow in making headway.

Ironically, New Zealand has very few babies weighing under 2.5kg at birth despite our high infant mortality rate.

Although low birth weight is regarded as an indicator of poor nutrition in developing countries, Auckland University obstetrician Professor Lesley McCowan said New Zealand's low rate of low-birthweight babies was more because of ethnic factors.

"Pacific Island families have larger babies, so that increases our average birthweight," she said.

New Zealand's immunisation rates for toddlers aged between 12 and 23 months has increased faster than most other countries between the two Unicef surveys - from 84 per cent in 2002 to 92 per cent in 2010. But it is still the lowest of the eight countries in our comparison.

Advisory Centre director Dr Nikki Turner said some districts had already reached the national target of 95 per cent and the target could be reached on a national basis this year.

"We started way back," she said. "We have actually made strides over a lot of other countries. We are doing as well as, or slightly better than, Australia at the moment."

She said the improvement showed what could be done with a determined focus on a child health issue. "It's recognising it's an issue, measuring it, monitoring it, managing it at every level and getting good feedback loops. It's a whole system approach."

New Zealand 15-year-olds' average scores in the international "Pisa" tests for reading, maths and science literacy are still fourth-highest in the world, behind only Finland, Japan and Canada.

Auckland University educationalist Professor Peter O'Connor said the record showed "the quality of our public education system which relies on highly qualified teachers delivering a national curriculum that is well understood and respected".

Another international survey, "Timss", found recently that Kiwi 9-year-olds finished last equal in maths among developed countries. Education Minister Hekia Parata said she was considering a return to basic arithmetic drills to complement more theoretical approaches to maths teaching in schools.

But Professor O'Connor said the Pisa results suggested that most students were doing well by age 15.

"Both Pisa and Timss suggest that we have high achievement but low equity," he said.

The Unicef figures suggest a leap in teenagers staying at school or in further education, likely reflecting both increasing skill needs in the economy and the recession, which has made it much harder for young people to leave school and find jobs without further training.

But, although those still in education leapt from 66 per cent of the 15-19 age group in 2003 to 81 per cent in 2010, this was still below 25 out of 34 other developed countries.

New Zealand really is "clean and green" by the standard used in this report: average annual concentration of fine particulate matter in the atmosphere.

Our rate of 12 parts per million is cleaner than all other developed countries except Australia and Estonia.

But Massey University ecologist Dr Mike Joy, who recently questioned New Zealand's "100 per cent pure" slogan, said this was purely an accident of geography.

"There are places in Auckland that are really high, but if you take some kind of an average over the country, it's a windy, oceanic country and it doesn't surprise me at all," he said.

"In the case of Australia, it's very sparsely populated.

"You can have really high concentrations in one place, but if you average it out across the whole country you get away with it."

Homicide and air pollution are included in the report as indicators of the broader environment in which children grow up. New Zealand's rate of 15 homicides a year for every million people is higher than any other in our group of eight countries except the United States.

However Phil McCarthy, a former Corrections Department general manager of prisons and now director of Rethinking Crime and Punishment, said the figure of 15 homicides per million in 2009 was an unusual outlier on recent years.

"Our average over the last few years is more like 11 or 12. That puts us dead on the United Nations figure for the Western European average," he said.

Only nine of the 35 countries have rates below 10. Most range between 10 and 20, and the United States is an extreme outlier with 49 homicides for every million people.

New Zealand's teen birth rate is the other half of the "NEET" story. Our 26 births for every 1000 girls aged 15-19 is higher than all other developed countries in the survey except Britain, the United States, Bulgaria and Romania.

This figure has not dropped significantly since then and was still 24.9 for every 1000 girls last year.

Strive Community Trust chief executive Sharon Wilson-Davis, who was a member of the Government's welfare working group, said the domestic purposes benefit (DPB) contributed to our high rate.

"It's a lack of hope," she said.

"It's: 'If I can't get a job, and I don't like school, and my parents are pretty stuffed up, I can at least get the DPB'. And it's all that stuff around having someone I love, if they have gone through all sorts of mental and physical abuse.

"I'm hopeful that the reforms that have come about with the welfare system might cut that."

By Simon Collins Email Simon