Whakaari, a centre, has been playing league for three years.
"I was excited when I was told, it's something I've always wanted," Whakaari said.
"The (Sydney Rooster) coaches were helpful, the whole team was pretty close and I really liked the culture."
Whakaari plays for Pikiao and is in the New Zealand Maori U16 Rugby League team. He was selected to play in the Pasifika Youth Cup in January and has a scholarship to attend the NZRL National High Performance Club next month.
He also plays rugby union and is part of the Rotorua Boys' High School 1st XV which represented New Zealand at the Sanix World 1st XV Tournament in Japan last year.
Sydney Roosters recruitment manager Adam Hartigan said fewer than five youngsters were given this opportunity throughout New Zealand and Australia each year.
"He fits our recruitment (needs). He's big, athletic, has good skills and we are really pleased he is a Rotorua Boys' High School boy because the school is big on discipline."
Hartigan said they needed to ensure their players' on-field behaviour matched their off-field behaviour, particularly because the contract was Sydney-based and Whakaari would still be living in Rotorua.
"It's refreshing to know a boy like Rayna has got his life sorted on and off the field and a lot of that comes down to discipline at his school."
Whakaari's manager, Daniel O'Loughlin, said the teenager had been identified as a "high end talent".
The two-year contract meant he was still free to explore other options at the end of the two years if he wanted to pursue being a Chief or an All Black instead.
"It means they (the Roosters) can keep him on their books and build a relationship. If he has seven or eight clubs chasing him later on the Roosters can get in front of him first.
"He's a lovely kid and has a great family. It's great news."
Rotorua Boys' High principal Chris Grinter said it was a great opportunity for Whakaari.
"For the school to be recognised by professional clubs and teams it's obviously a credit to the programmes and academies we are running here at school," Grinter said.
"Rayna follows on from other students of ours over recent years who have been approached and signed up on different sporting contracts and I know this will continue going forward. It's a great pathway for the boys."
Whakaari follows in the footsteps of former Boys' High student, Reuben Te Kani, who moved to Australia last year to play for the Canterbury-Bankstown Bulldogs under 20s squad.
