Yesterday, students and staff at the school south of Auckland, were stunned by his sudden death.
One of his teachers, Richard Smythe, said Lomu at first showed no interest in rugby.
"He was always telling me he was going to run away from the school in the weekends and go and play league with his mates."
Smythe said the first time Lomu played rugby, there was "nothing".
"But the following week when we repeated it... Jonah put on the jersey - for five minutes it was supposed to be -but he kept getting these tries.
"And so he stayed for the whole half-time... he had great big long arms... even as a junior there was only one way to stop him, to tackle him at the legs.
"I just remember the coach saying 'where did you get that monster from?' - and I said 'that monster's from Māngere'," Smythe said.
But his teachers said off the field, Jonah Lomu was anything but a monster.
"Despite his size, he was easy to talk with - to get on with - looked after the juniors in the school when he was a senior in the college, just someone who was genuine," another teacher Chris Bean said.
"It was obvious he was an outstanding football player, that just needed to be guided by the right people... he was certainly destined to be an All Black."
Bean said Lomu was a gentleman off the field, a kind-hearted and soft-natured child who didn't like to tower above other students - but who could not help it, because of his size.
Rugby was not Lomu's only strong point - he liked art and painting, and an unsigned piece of his still hangs in the school hall.
Photos of him with his rugby teams throughout his years at the school are hanging there too.
Lomu also excelled at athletics, described as a "human dynamo".
Smythe recalled Jonah running the 100 metres. "I had to time it - I just made certain I was never in his way. He was literally shoulders and heads above everybody else dashing to that 100 metre line."
Lomu rarely showed any anger, but Smythe remembered one incident that he said also stayed in Jonah's mind.
"Jonah was on the rampage, one of the few times he really got mad - and he was going through the dormitory, all the boys ran away because he was so angry.
"Somebody had stolen $10, so my son Sione went up and picked up the $10 that he found behind the door, and said 'Jonah is this your $10?'
"Well, after the 1995 World Cup, Jonah decided he'd come up and pay a visit in his fancy car... he said "Sione, Sione.. do you remember the $10?'
"'Jump in the car, we're going down to KFC'. And Jonah told Sione to just buy boxes and boxes of KFC for all the boys in the dorm," Smythe said.
"Jonah said 'payback time, that's the payback for the $10'."
Smythe said students were subdued after learning Lomu had died.
"They're very proud of Jonah as being one of them, they felt it in their silence, just standing around, not their usual jumping around.
"I walked into my classroom, and there was something like 36 students, all quiet," he said.