“We will be running a blitz on this over the next few weeks and working with those students and families who are consistently late for this reason.”

Lateness impacted not only the student but also the class and teachers, the post said.

“Being just 10 minutes late every day adds up to an hour a week of lost learning. Over a year this adds up to one week of school missed in a year!”

The post warned that being late for class meant important instructions could be missed and children may feel uncomfortable and on the outer with peers.

Students were reminded to arrive on time – at least five minutes before the 8.30am bell.

The school told the Herald it was too early to tell if the message – posted Monday – had had a positive effect, and declined to comment further on the planned crackdown.

Ministry of Education spokesman Sean Teddy said schools develop their own policies on what constitutes lateness, and ministry guidance suggests marking students who are more than 10 minutes late with an L code.

Teddy said the code would help the school monitor and respond to patterns of lateness.

Clinical psychologist Dan Ford told the Herald the best way for parents to help young people get to school on time was to make sure they got up at the same time every morning – even on the weekend.

Ford – clinical director of The Better Sleep Clinic in Auckland – said young people needed consistency to get into good sleep habits.

“Shifts in the body clock happen in puberty so we often see … difficulties falling asleep from 10-11 years of age,” Ford said.

Up to the age of 13, it’s recommended young people need nine-11 hours of sleep each night. From 13-17 this drops to eight-10 hours.

Even if a young person had a late night it was still important to get up at the same time the next day – even if getting through the day was a bit tougher.

“Waking time is a lot more important than what time they go to sleep.”

Ford said if an intermediate school student needed to get up at 7am to be at school on time, they needed to aim for a 10pm sleep time.

Older teens might go to bed later but it was still important to wake up at the same time each morning.

Getting out into daylight as soon as possible in the morning and getting around 16 hours of daytime activity was also important.

Ford compared sleep to hunger and said just like working up an appetite through being active during daylight hours, physical activity and waking at the same time each day prepared the body for sleep.

He also recommended giving a bedtime – even for older teens.

“There might be some resistance to this but the emotional upset from being given a bedtime is not as bad in the long term as the upset from having poor sleep.”

Avoiding screens when in bed was also important, he said.

“Teen eyes are very sensitive and the messages they get sent through their phones means they are constantly being alerted to something.

“It’s addictive and has an alerting effect on the brain which affects sleep.”

Having a central charging port in the home that couldn’t be accessed after bedtime was also a good strategy, he said.