"This child asked the man for the password and, of course, the man didn't know it, so the child ran home.
"Unfortunately, he didn't inform Mum, who was at home, mainly because he was worried about upsetting Mum."
After lunch on Tuesday, the boy was worried about walking home, so told his teacher what happened.
The school will have more staff out, and are reminding parents to speak to their children about safety.
"We're just reminding our parents to talk to their child about what they need to do to keep themselves safe if they ever get into this situation."
Su'a said the boy "did really well".
"He was pretty brave."
She only wished he'd told his mother as soon as possible about the approach, "because then the police could have been notified and the perpetrator could have still been in the vicinity, and the likelihood of actually nabbing him could have increased".
Su'a said another Upper Hutt school last week reported a similar approach.
The password system involves parents giving their child a password that another person picking up the child has to say so he or she knows it is safe to go with them.
Detective Senior Sergeant Mike Sears said police were aware of three incidents in Upper Hutt where children have been approached by an unknown man in the past month.
"Police take any report of this type extremely seriously and continue to investigate two of these incidents," Sears said.
"In an incident that occurred on March 13 on Fergusson Drive, the person involved has been identified and police have established there was no criminal element involved. All parties have been spoken to and advised of the outcome."
A further incident occurred outside Upper Hutt Primary School on March 28 where a child was approached.
Sears said specialist interviews have been conducted with the child, and police are currently reviewing the information.
"Police are following positive lines of inquiry," he said.
"Police are conducting interviews and enquiries in relation to a third incident that occurred yesterday in Trentham near a local primary school where a student was approached and spoken to by an unknown male.
"Police are reviewing evidence and at this stage cannot confirm if there is a link between any of the incidents.
"Patrols have been increased in the area and the schools and families involved are being spoken to and we are working closely to support them.
"Police remind the public to contact them immediately should they see anything suspicious."
What can children do to stay safe?
• Walk home with someone else
• Stay on the footpath
• Move away from the edge of the footpath if a car pulls up
• If approached by a stranger, continuing walking or run away
• Use a family password
• Make plenty of noise if grabbed by someone
• Tell an adult as soon as possible