Nearly two-thirds of London's new or refurbished schools are not fitted with potentially life-saving sprinkler systems, the London Fire Brigade (LFB) has warned.
According to the LFB, every year one in eight schools nationally suffers a serious arson attack, but despite the introduction of Government guidance three years ago, too many schools do not have sprinklers.
Fire chiefs are consulted on the plans of every new-build or refurbished school in the capital, but 48 out of 79 school building projects seen by experts did not plan to have the systems in place.
Sprinklers prevent fire from spreading and "greatly reduce the chance of death or injury", the LFB said.
Recent national figures show the police and fire brigade were called out 1,000 times over two years due to school arson attacks.
The cost of school fires is around #163;65 million a year, with London accounting for more than a third of the cost.
But, as well as a huge financial impact, the LFB said the fires can have a "devastating impact" on the community as a whole.
Councillor Susan Hall, chairman of the London Fire and Emergency Planning Authority's community safety committee, said it was time building owners and developers stopped playing the "high-risk game", gambling that there will never be a fire in their building.
"For too long, architects and developers have ignored the overwhelming benefits of sprinklers in reducing the damage and potential loss of life a fire can cause," Councillor Hall said. "A fire that destroys a school devastates the local community."
Earlier this month, the fire brigade was called to Crofton Junior School in Bromley, south-east London, to deal with what investigators believe was an arson attack.
A spokesperson from Partnerships for Schools, the Government's delivery agency for capital investment in schools, said: "It is for local authorities and other promoters of schools to carry out risk assessments, and ensure that sprinklers are installed where deemed necessary. All schools should have adequate fire precautions in place to safeguard life in the event of a fire."