The trial has been backed by parents at Kaihere School in the Hauraki Plains, which is near a blind rise on a 100km/h stretch of State Highway 27, about half an hour north of Morrinsville.
On school days, the speed limit is lowered to 70km/h between 8.25am and 9am, and from 2.55pm to 3.15pm.
Principal Carolyn Morris said it had made a big difference to traffic speeds.
Parents used to hold their breaths as they waited and listened for oncoming traffic, but now they had peace of mind when pulling out of the school car park.
"It's been hugely successful. Parents have told us that they feel a lot safer, particularly pulling out onto the road," Ms Morris said.
"I really hope it does continue because it's made a huge difference for our school."
Ms Morris said more could be done, including a wider waiting bay for traffic turning right into the school.
But she thought other rural schools would embrace variable speed limits.
Waikato's Te Uku School, which is on a well-used stretch of State Highway 23 near Raglan, is also in the trial.
Principal Rachel Allan said the community had been asking for a lower speed limit for years.
Now the school is able to lower the speed limit from 80km/h to 60km/h between 8.30am and 9am, and from 2.45pm to 3.10pm.
The school could also lower the speed limit whenever there was an event or sports match.
"We know that it has made a difference, because we notice that cars go past at a slower pace," Ms Allan said.
"Over a long period of time the community has been asking for a reduced speed limit in this area, and now that it's happened, it's really pleased a lot of people. We're just much, much safer exiting and even entering our school entrance."
The expanded trial is part of a wider rural school safety programme launched today.
Mr Bridges said the NZTA would work with the Ministry of Education, local councils and police to identify how to improve safety at high-risk schools.
Guides for high-risk schools would be developed for use by communities, schools and road controlling authorities - firstly for rural schools, and then for urban schools.
AA principal advisor Mark Stockdale said the proposals would target risks and improve rural road safety for children and other road users.
He said improving safety was about more than just speed limits.
"Independent research shows the best thing that can be done to reduce accidents around schools is to eliminate the need for children to cross the road.
"That includes things like creating bus bays that are off the road, moving the school gate off the main road, and providing enough car parking for parents on the same side of the road as the school."
