Detective Sergeant Grayson Joines told the Herald on Sunday the 12-year-old was sitting on the skylight when he fell through it.
"The poor little fellow has gone feet up in the air and fallen about 25 feet. He landed on a pretty hard concrete floor with carpet on it."
His mates rushed to him, smashing a locked classroom door. Police arrived seconds later.
"When the police got there they saw the broken door and the two other boys dragging their mate, who was near unconscious, out of the building. They were distraught as hell, they were pretty close friends. They are concerned about their little mate, who's not in a very good way," Joines said.
Makere travelled with him and has been at his bedside. "[His] mum's standing up pretty well."
Police believe the boys had not been up to anything malicious or criminal at the school.
"Kids are kids, kids try things, kids have fun and kids explore. Sometimes it's safe and sometimes it's not," Joines said. "They'd probably done it heaps before but this time it went terribly wrong. They were just mucking around, as boys do."
Joines said the boy and his friends were not pupils of the school.
Principal Shona Oliver said she could not comment on the incident as police were investigating.
"For us, it's just very sad for a family at this time of year," she said.
Last month, Timaru teenager Jordan McKeown died after he fell through a skylight at a local arcade.