A sex education programme which initially ruffled some feathers because of its risqué content will be rolled out in schools across the country.

The ACC programme "Mates and Dates" was launched at eight New Zealand secondary schools in 2014. It followed the high-profile Roastbusters scandal, in which several West Auckland boys bragged on social media about having sex with intoxicated underage girls.

It also coincided with a parliamentary inquiry which said schools needed to start teaching students respectful attitudes to sex and sexuality instead of just the mechanics of sex and reproduction.

Since the original pilot scheme, Mates and Dates has been trialled at a total of 133 schools, with rolls of 36,000 students.

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The programme consists of five hour-long sessions on healthy relationships, consent, gender and identity, what to do when things go wrong, and how to keep safe. It has involved interactive elements including a dissection of Robin Thicke's controversial music video Blurred Lines.

There were some teething problems during the programme's pilot phase. A few teachers complained that it made classes unruly and that some of the sexual material was confronting for more conservative students.

Despite those initial hurdles, later reviews found that a majority of students had responded positively to the programme.

ACC injury prevention manager Mike McCarthy said the corporation's board had now approved additional spending of $18.4m to expand it to 180,000 students around the country.

It is one of several preventative measures ACC is backing in a bid to reduce mental and physical injuries caused by sexual violence.

The number of sensitive claims – which relate to injuries from rape, sexual assault, and child abuse – has risen by 88 per cent in the past five years because of more generous state support for victims and movements like #MeToo. Treatment costs alone passed $50m last year, up from $12m in 2013.

ACC data shows sexual violence rates are highest among people in their late teens and early 20s. The data is based on when people make a claim, and the average delay between an assault and a claim in New Zealand is 16 years.

"It really indicates that we've got some pretty significant child abuse problems in our country that we haven't looked at in that sort of holistic, cultural way in New Zealand society," McCarthy said.

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"That's the biggest nugget here – that culturally we've got some stuff happening that we don't talk about or accept.

"We then see it down the track, where people start seeking help, but we're not actually addressing it right back at the prevention point."