Robbie Turner still scratches his head at how his little buddy, 13-month-old Niko Guttenbeil, managed to shrink between visits to Grey Lynn Primary.
The 10-year-old is part of a programme run by Barnardos in 35 Auckland schools known as Roots of Empathy, in which babies become "teachers" in classrooms.
Parents such as Niko's dad, Sky TV commentator and former Vodafone Warriors player Awen Guttenbeil and his wife, Natasha, visit for 27 sessions, helping children to learn about a baby's development, what not to do, and to observe and interpret the baby's communication.
Highlights for Robbie have included cuddles, but weighing and measuring his mate was confusing.
"It was real weird because he actually shrank a centimetre, so I don't know whether it was a dodgy measuring tape or anything, but he shrank.
"I learned about how their brains are really precious - they need to be in a safe house because they can't bump their heads and they can really hurt their brain."
The Guttenbeils' daughter Mila, 6, attends the same school. The couple decided the Roots of Empathy programme was important to support given NZ's child abuse statistics.
Awen Guttenbeil said the pupils' reactions were "precious".
"I've noticed the kids take so much more interest in Niko when he comes to school outside of the groups. They're always wanting to know about his development - that has been really nice to see they have this really nurturing side to them."
Natasha Guttenbeil said a baby's ability to teach was a simple idea. "It's amazing to see children make the connections. They learn things like about baby's pincer grip. It teaches that a crying baby isn't a naughty baby, it's just a baby with a problem."
The pupils' discussions often turned to the baby's feelings and family life, and Mrs Guttenbeil wondered if it touched a few nerves with children who might not have ideal home lives.
"I'm not a perfect parent at all but they get to see someone being loving to a baby, not getting mad at them when they cry."
Feedback from schools included children being more focused, being able to resolve their differences by themselves, increased self-confidence and reduced bullying.