Even promiscuity is waning. The number of high-school students who have never had sex have increased from 68.7 per cent in 2001 and 63.7 per cent in 2007 to 75.6 per cent, and the number described as currently sexually active dropped from 21.2 per cent and 26 per cent to 18.8 per cent.
Principal investigator Dr Terryann Clark said the surveys showed that public health messages about the risks of binge-drinking, drink-driving and smoking were getting through.
"This cohort of young people have essentially had smokefree environments, smokefree schools, they have really not been exposed to smoking in the same ways that previous generations have been," she said.
"We need to pat ourselves on the back and say these things are finally starting to work."
A Unicef survey of 29 rich nations this year found that fewer young people were using alcohol, tobacco and marijuana in almost all countries, but Dr Clark said the declines in New Zealand were "way more dramatic than any other country we have found information on."
"I think there is something about being a small country. We are able to implement programmes and policies a lot faster," she said.
But she said the findings on depression and self-harm showed that teenagers were still feeling stressed and pressured.
"There has been pretty much no change in depression, and particularly for girls that has gone up," she said.
Students at Edgewater College in Pakuranga said they were not surprised at the high rates of self-harm.
"Especially with the juniors it's quite common; it seems to fade out in the seniors," said Mackenzie Valgre, 16. "I have a few friends who have quite seriously self-harmed."
She said her sister, an intermediate school student, had seen a group of girls meeting regularly outside the toilets at lunchtimes with scissors.
But Jonelle Rangikotua, 15, said some teenagers cut themselves "for show" and it was hard to tell who was genuinely depressed.
"People might see it and think, 'Oh it's common, I should do it,"' she said.
Selvi Balasubramaniam, 16, said she read on the social media site Tumblr that it was more accepted to be insecure than to be confident.
Mackenzie agreed: "If you look at Tumblr, it's become almost fashionable.
"If you say I'm happy with my body and confident with who I am, they say, 'What do you mean'?"
But they said other girls cut themselves because of problems at home or because of worries about their body image.
"You are replacing the emotional pain with physical pain so it distracts you from your problems," said Mackenzie.
• Almost half (42 per cent) of Kiwi teenagers are of mixed ethnicity, up from 29 per cent in 2001 and 39 per cent in 2007.
• Three-quarters (73.6 per cent) still count European as one of their ethnicities, much the same as in 2001 (72.6 per cent) and 2007 (75.7 per cent). One-fifth (20 per cent) have Maori ethnicity, 17 per cent Pacific and 15.2 per cent Asian.
• Three-quarters (78 per cent) were born in NZ, down from 89 per cent in 2001 but up slightly from 76.4 per cent in 2007.
• Samoans were the most likely of the main groups to say they were very proud of their family's culture (87 per cent), followed by Tongans (86 per cent), Cook Islanders and Niueans (both 81 per cent), Europeans (73 per cent), Maori (72 per cent), Indians (64 per cent) and Chinese (57 per cent).
• More than a quarter (29 per cent) of teens live in more than one home, usually because their parents have separated - the same as in 2007. Ninety per cent (unchanged) have a mother who acts as a parent for them but only 72.9 per cent (down from 76.4 per cent) have a father who acts as a parent.
• Most teens say they get enough time with their mother sometimes or most of the time; the number saying they "hardly ever" get enough time with Mum dropped from 14.2 per cent in 2007 to 10.8 per cent.
• Teens get less time with their fathers but the number who "hardly ever" get enough time with Dad was stable at 23.8 per cent.
• Unemployment has increased since recession hit, but the number of teens who have no parent in paid work is still surprisingly low at 3.6 per cent, up from just 1.8 per cent in 2007.
• Secondary school students themselves are much less likely to have a part-time job - down from 42 per cent in 2001 to 39 per cent in 2007 and just 26 per cent last year.
• However even working families are feeling the pinch: 11.5 per cent of teens say their parents worry about not having enough money for food "often or all the time", up from 8 per cent in both the last two surveys; those who never have to worry about money for food dropped from 64.4 per cent to 55.7 per cent.
• There was no significant change in families averaging more than two people per bedroom (5.5 per cent) or where some people sleep in the living room (12.1 per cent), in a garage (6.2 per cent) or in a caravan (1.3 per cent).
School
• The vast majority (82 per cent) of teens have only ever attended one secondary school; 13.2 per cent had been to two and 4.8 per cent had been to three or more.
• Teens are more likely to like school a lot (29.1 per cent, up from 23 per cent in 2007), and less likely to dislike it (down from 14.5 per cent in 2001 to 12.2 per cent in 2007 and just 9.8 per cent this time). The other 61.1 per cent like school "a bit" or think it's "OK".
• They are more likely to think teachers, coaches and other people at school care about them a lot - up from 23.2 per cent in 2001 to 25.1 per cent and 27.2 per cent in the two latest surveys.
• They are more likely to think teachers are fair most of the time - up from 42.8 per cent to 48.8 per cent and to 51.7 per cent in the latest survey.
• Almost all teens (86.9 per cent) feel safe at school all or most of the time, up from 78.1 per cent in 2001 and 83.5 per cent in 2007.
• Those who are bullied at school at least weekly has stayed low at 6 to 7 per cent in all three surveys. Those who didn't go to school at least once in the last month because of bullying plunged from 9.5 per cent in 2001 to 4.1 per cent in 2007 and ticked up only marginally to 5.3 per cent this time.
• One-seventh (14.4 per cent) of girls and one in 11 boys (9.2 per cent) received nasty or threatening messages on their mobile phones in the past year; 10.8 per cent of girls and 7 per cent of boys received such messages via the internet. The numbers were similar in 2007.
• Teens are becoming much less violent. Boys who hit or physically harmed another person in the past year dropped from half (51.1 per cent in 2001 to 47.9 per cent in 2007 and just a third (34.1 per cent) in the latest survey; girls who hit or harmed someone fell from 39.7 per cent to 33.2 per cent and now just 24 per cent.
• Boys who got into a serious physical fight in the past year fell from 27.9 per cent in 2001 to 26.2 per cent and now just 19.6 per cent; girls in fights declined from 14.5 per cent to 12.2 per cent and now 9.6 per cent.
• Around a quarter of girls in both the first two surveys (26.4 per cent, then 24 per cent) said they had been touched in a sexual way or made to do unwanted sexual things. That dropped to 19.5 per cent in the latest survey.
• Three out of every eight teenage girls (37.8 per cent) are overweight or obese, up from 34.7 per cent in 2007.
• Boys who are overweight or obese crept up more slowly, from 34.4 per cent to 35.4 per cent.
• Most (68.5 per cent of boys and 56.5 per cent of girls) are doing at least 20 minutes of vigorous physical exercise at least three times a week, little changed from 2007 and more than in 2001.
• More are buying lunch from shops and takeaway bars than in 2007 - up from 35.9 per cent to 43.2 per cent for boys, and from 33.7 per cent to 35.5 per cent for girls.
• But overall the numbers eating fast food at least four times a week have halved from 12.8 per cent to 6.4 per cent, and the numbers drinking fizzy drinks at least four times a week have more than halved from 29 per cent to 12.3 per cent.
• A lot more are using the internet at least an hour a day - up from 18.2 per cent in 2001 to 51.6 per cent in 2007 and now 67.6 per cent. Those watching TV for at least an hour a day rose from 55 per cent to 73.2 per cent between the first two surveys but have dropped back to 64.6 per cent in the latest survey.
• More than half (55.1 per cent) of boys, and 43.5 per cent of girls, are very happy or satisfied with their lives - both up slightly from 2007. Most of the others say life is OK, but 6.2 per cent of boys and 9.8 per cent of girls are not very happy or unhappy.
• One in six girls (16.2 per cent) and one in 12 boys (8.6 per cent) show significant depressive symptoms. These numbers have fluctuated with no obvious trend over the three surveys.
• Teens who have deliberately harmed themselves in the past year have risen since 2007 from 26 per cent to 29.1 per cent of girls, and from 15.5 per cent to 17.9 per cent of boys.
• However those who attempted suicide in the past year were stable at 6.2 per cent of girls and 2.4 per cent of boys.
• Chastity is making a comeback. About a third of secondary school students in both the first two surveys (31.3 per cent, then 36.3 per cent) had had sex, but the number dropped in the latest survey to 24.4 per cent. However only 58.2 per cent of those who are sexually active always use contraception, about the same as in the first two surveys.
• Binge-drinking in the past four weeks has almost halved from 40.1 per cent of teens in 2001 to 34.4 per cent in 2007 and 22.6 per cent in 2012. Boys (23 per cent) and girls (22.2 per cent) are now almost equally likely to binge-drink.
• Drink-driving is also falling. Teens who were driven in the past month by someone who had been drinking declined from 27.8 per cent in 2001 to 23.2 per cent and now 18.4 per cent.
• Teens smoking cigarettes at least weekly have collapsed from 15.5 per cent to 7.8 per cent and now just 4.5 per cent.
• Teens smoking marijuana at least weekly have halved from 6.7 per cent to 4.7 per cent and now 3.2 per cent.
• Three-quarters (74.2 per cent) of teens in the latest survey had seen a family doctor in the past year, down from 83.5 per cent in 2007.
• Almost a fifth (18.6 per cent), up from 16.8 per cent in 2007, were unable to access healthcare when they needed it at least once in the past year. Of these, 51 per cent simply hoped they would get better, 46 per cent didn't want to make a fuss, 30 per cent were too embarrassed, 28 per cent didn't have transport to get there and 26 per cent said it cost too much.
• Spiritual beliefs are still very important for 28.1 per cent of teenagers, down slightly from 32.1 per cent in 2001 and 29.2 per cent in 2007.
• Numbers attending a place of worship at least once a week have been stable at 25.8 per cent in 2001, 28.8 per cent in 2007 and 25.8 per cent in the latest survey.
