Schools need to introduce education programs on sexual behaviour earlier, and parents need to take more responsibility to protect their teens, experts have warned.

On Thursday it was reported three boys, aged 14, had agreed to leave Cranbrook School after a sexual incident involving a 14-year-old girl at "a gathering".

The girl is alleged to have had consensual sex with one boy, and alleged to have engaged in other sexual acts with the two other boys.

Karen Willis, executive director of the Rape and Domestic Violence Service, said it took a horrific incident in Coffs Harbour for the NRL to deal with sexual behaviour issues in its code, and that schools needed to get on the front foot.

"If people worry about reputation, it only makes it worse," she said. "We can see that from the sporting codes' experience."

Most schools are attempting to address the issues thrown up by digital media and societal mores.

"Every school is speaking about the challenges of earlier sexualisation," said Jann Robinson, the chairwoman of the Association of Heads of Independent Schools in NSW. "In many ways there has never been a harder time to be a parent ... Parents are grappling with the forces of digital media – kids are being exposed to much more explicit stuff," she said.

Paul Dillon, a drug and alcohol educator, said that in his view there was a tendency for parents to want the school to take too much responsibility for shaping their teens.

"Teenagers aren't meant to like their parents. They're meant to love them, but not to like them very much. It's about parents setting boundaries and setting rules and sticking with them."

Mr Dillon suggested parents should always take their children to parties, pick them up and call the supervising parents in advance. He said the consequences of breaking the rules should be clearly stated.

Geoff Scott, president of the Primary Principals Association, said primary schools offer "generic" personal development courses and subjects like social relationships from year 3, but the responsibility for educating children still lies predominantly with parents.

"For any given class of 30 students, you might have quite a number who are on Facebook, even though they shouldn't be, when they're under 13, or getting on to their older sibling's Facebook sites, or encouraged by parents even sometimes when they shouldn't."