Belmont schoolchildren are helping to make the once-dangerous roads outside their school safe.
The year seven Belmont Middle School pupils have been acting to cut traffic and illegal parking on narrow Hibbert Road.
Interim deputy head, Patricia Rogers, who was once knocked down by a car outside the school, said: "It used to be absolute chaos."
A pregnant mother was also bumped while picking up her children. Fortunately she was not hurt.
The problem had been parents parking their cars for a second to drop their children at the school gates.
Other cars would then mount the pavement to try to pass, or attempt a U-turn.
Some parents also parked across locals' drives, blocking them.
Now, every Friday morning and afternoon, the year sevens stand outside the gates - no matter what the weather - and monitor traffic.
If they spot a car stopped on a double yellow or a zigzag line, they walk over in high visibility jackets and tell the driver this is illegal.
Mrs Rogers said: "The children have gone about it in a really grown-up and responsible way. It has taught us that if we do things well we will have a positive impact on society."
The children and Mrs Rogers want Harrow Council to make the road one-way.
And though most parents think the scheme is great and support it, Mrs Rogers said some could do better: "Monday to Thursday many parents do park elsewhere but of course there are some who make the most of pupils not logging number plates and continue to park to drop off."
Local police support the pupils, have spoken to the children about the rules of parking, and visit the gates regularly. The parking enforcement team has also sent a car with a camera. But Mrs Rogers believes the 'biggest impact has been the pupils'.
The campaign started because Mayor of London Boris Johnson wants every school in London to produce a 'travel plan' this year.
Every school in Harrow has been given the task of writing a plan that will reduce school-run traffic and get pupils to school in alternative safe ways, such as on foot or by bike.