Rainger says it was an easy team to captain. Though not necessarily favoured to win the title at the start, they stuck tight and performed when it mattered.
"I have to give credit to everyone in our team, especially the fast bowlers Luke Guilford and Henry King," he said.
"They destroyed teams at the top of the order and that put them under pressure, allowing us to set aggressive fields and have aggressive tactics. That paid dividends in the end."
Having just ended his second year in the First XI - last year he won the batting prize - Rainger is well placed to speak of the Auckland Grammar cricket and sporting culture.
"Playing for the Lion is something unique and different. Everyone just gives more than 100 per cent. [Director of sport] Mr [Grant] Hansen told us, 'The Lion never backs down'. So playing for your school is second to none."
"They were a great bunch of guys. When we were serious, we were focused, and when we switched off, we could have a laugh."
Rainger tended to throw out the anchor at the top of the order, but he is more than an accumulator. Last year, he struck 134 off 132 balls for the First XI against Scots College in Sydney - the school he attended before coming to Auckland Grammar.
"[Accumulating] is something that comes naturally. But you play to the conditions and if you feel positive, you can sometimes be the aggressor."
Though he didn't register a century this year, he was consistency personified with several 50s and a high score of 94.
As he is a leftie and one who uses Gray Nicholls bats, it is not entirely surprising that Rainger rates England captain Alastair Cook highly.
"One part of being captain is being cool under pressure. Obviously he's been under a lot of pressure, but he doesn't seem fazed by it. I try to follow that ... and besides, us lefties have to stick together."
Coach Mark O'Donnell, who has coached Auckland and helped with the Black Caps, was another big factor in the Auckland Grammar success.
"He's coached the likes of AB de Villiers and Virat Kohli, some of the best in the world. Technically and strategically he was a huge help."
He also paid tribute to Parnell coach Ian Trott, father of former England batsman Jonathan Trott.
"I've worked with him for a long time. He keeps it simple and he's a great guy."
On the immediate horizon for Rainger is getting into the New Zealand Under 19s, but he hopes to get in a few games for Parnell, Eastern Districts Under 18s, for whom he is playing for the third year in a row, and the Future Aces XI.
Then it will be a change of scenery when he heads to Wellington in February to take a conjoint BCom and LLB degree at Victoria University and play cricket for the Karori club.
"Wellington looks like a cool city. If I can get into the Wellington cricket system, that would be great."
The Auckland Grammar First XI has a core group returning next year, so Rainger feels they'll be in good shape to defend their title.
"They're a good bunch of guys and I'm sure they'll do the job."
Rainger had the misfortune to be up against Sacred Heart captain Glenn Phillips for the boys' cricket award at the ASB Young Sportsperson of the Year night. Rainger rates his counterpart highly and Phillips took Sacred Heart to the runners-up position, scoring a century against Auckland Grammar in the process.
Rainger was vice-captain under Phillips of the Auckland Schools side which beat their Christchurch counterparts this year.
He says he can switch on and off as required with his cricket and studies, not to mention a stint on the wing for the championship-winning Auckland Grammar 4A rugby team. It all added up to a very busy, very successful year.
