“I find it really upsetting when you break the speed limit. Lots of my friends cross this road, and you might have knocked one of them over.”

Eleven-year-old Victoria Rogers is quietly chastising a driver caught speeding outside her school. More effective than speed cameras and less expensive than a ticket or fine, is the unfailing power of guilt.

Shamefaced, the driver apologises before moving slowly away.

Victoria, along with 10 of her Year 6 classmates at Wick Marcross primary, in the Vale of Glamorgan, has teamed up with south Wales police and the Safety Camera Partnership for a road-safety initiative dubbed “the short arm of the law”.

Earlier this summer, a former pupil was knocked down by a car on the busy road outside the school. Police cameras have recorded drivers accelerating through the 30mph zone at speeds of up to 72mph, regardless of warning signs and strategically placed police vans.

Roger Lewis, the school’s headteacher, contacted local police, to try to reach a solution. They decided to team traffic officers with a group of Y6 pupils.

Drivers caught speeding outside the school would be forced to submit to a lecture from the pupils in addition to an official caution from the police.

Sergeant Gary Smart, who stood by while pupils addressed errant drivers, said: “The children are speaking from the heart. They say, ‘you could kill me if you drive like this’. It has a sobering effect, and more educational impact than getting a pound;60 ticket through the post.”

Roger Lewis believes that the mini-lectures also allow drivers to appreciate the impact they have on young children. “Look at the size of the children, especially those in reception class,” he said. “If a lorry goes past it’s a very intimidating experience.”

Since the project began, he says, the road outside the school has felt noticeably safer. He hopes that drivers have now been embarrassed into re-thinking their actions.

“They know they are doing wrong. But when they’re told by a child that they’re doing wrong it’s very humbling.”

Pupils have also taken the message home, lecturing their parents against the perils of speeding. It is this element of the project, rather than the central road-safety message, that has had the greatest impact for them.

Eleven-year-old Daniel Wilkinson said: “I usually get told off by my mum.

It’s a bit different telling an adult what to do for once. It felt good.

“I was probably more effective than my mum. She just tells me to go to my room.”

Victoria Rogers agreed: “If a child tells you off, you listen because it’s unusual. And children are also listening. They think before they cross the road so they’ll be safer. It makes you feel powerful.”