On some of the busiest school routes, about half of all buses will be designated to students, Transport for London (TfL) has announced.
The buses will be marked with a “schools service” sign, it added.
Taking effect from Tuesday, the buses will run on weekdays between 7.30am and 9.30am, and 2.30pm and 4.30pm.
Regular commuters are being warned over increased waiting times during these periods.
The dedicated school buses can be filled to capacity, but limits remain on regular services, TfL said.
Meanwhile, all children aged 11 or older still have to wear face coverings on public transport.
Walking, cycling and using a scooter to get to school is being encouraged, to reduce pressure on roads, and an extra 230 buses are being added to certain routes.
Other non-school buses for the general public will have red signs to differentiate them and make it clear they should not to be used by pupils, TfL said.
Gareth Powell, TfL’s managing director of surface transport, said: “Changes on this scale have never been made to the bus network before and we need everyone to do their bit to ensure children can safely return to school.
“It will greatly help if people can travel outside the peaks or walk, cycle or scoot wherever they can.
“Our transport network is the cleanest it has ever been, with extensive and frequent cleaning taking place, and our staff and police colleagues are out across the network to help and to ensure everyone understands the rules on face coverings.
“September is always a challenge on the bus network and, given the circumstances, customers may need to wait a bit longer to board buses.”
About a quarter of a million children used buses to get to school in London before the pandemic struck, TfL said.