Good quality and comprehensive education programmes in schools can delay the first time a teenager has sex and reduce risk-taking behaviour, international studies show.
Their findings are backed by Family Planning chief executive Jackie Edmond who said programmes were most effective when they began before a young person first has sex.
"Comprehensive sexuality education aims to equip children and young people with the knowledge, skills and values to have safe, fulfilling and enjoyable relationships and to take responsibility for their health and well-being."
"Because sexuality education is much more than 'the birds and the bees' it should start young."
Ms Edmond said good sexual education programmes were age-appropriate and build up information and skills over the years.
They should also look at attitudes and values, knowledge and skills such as decision making, communication and resisting pressure.
She said sexuality education was also more effective when home and school contributed.
"Parents are the first sexuality educators of their children"
"Parents and caregivers also role model relationship behaviours, gender roles and expectations."
Hundreds of parents have this week expressed outrage at the appropriateness of some sex education classes after it was revealed one 12-year-old was so upset at what he had learned that his father withdrew him from the programme.
The boy's lessons included discussions about anal and oral sex as alternatives to intercourse and telling the students it was okay to play with a girl's clitoris as long as she consented.
Some feel this kind of education will lead students astray.
One pregnant 17-year-old told the Herald she lost her virginity at 14 - a year after teachers told her sex was okay as long as she consented to it.
However, international research indicates a good quality programme can have positive effects on teenagers.
American researcher Douglas Kirby, a leading expert on the effectiveness of school programmes in reducing teenager sexual risk-taking behaviours, studied 48 comprehensive sexual education programmes and found two-thirds had positive effects.
Forty per cent delayed sexual initiation, reduced the number of sexual partners, or increased condom or contraceptive use.
Nearly a third reduced the frequency of sex - including a return to abstinence - and nearly two-thirds reduced the amount of unprotected sex.
In New Zealand schools can decide the kind of sex education they want to teach, as long as they consult their communities first.
The result is widely varying degrees of education from school to school - with not all of the programmes necessarily reaching the "good quality and comprehensive" threshold.
A 2007 ERO report into the teaching of sexuality in years 7 to 13 found "the majority of sexuality education programmes were not meeting students' needs effectively".
DOES IT HELP?
International research shows good quality sex education programmes can:
* Delay sexual initiation.
* Reduce the number of sexual partners.
* Increase contraceptive use.
* Reduce the frequency of sex, including a return to abstinence.
NZ sex education programmes:
* Vary greatly from school to school.
* Each school develops its own programmes with consultation with the community every two years.
* Teaching 12-year-olds about anal and oral sex and how to apply a condom is common.