Hackney Council believes there could be as many as 20 local yeshivot where children are being taught without the necessary state registration.
Under the law, children must be taught in a recognised institution until they are 16, even if it is independent.
But more than 1,000 strictly Orthodox boys from the age of 13 are still thought to be “missing” from the registered system in London.
Earlier this month, officials from the council and the Department for Education met to discuss how to encourage yeshivot to register.
It followed a visit to the borough a few weeks ago by inspectors from Ofsted, who were trying to locate unregistered premises.
Councillor Rita Krishna, the cabinet member responsible for children’s services and education, said: “Our main priority is ensuring pupils are safe and that they receive a high standard of education to give them the best possible start in life.”
Hackney Learning Trust was “working closely with the Department for Education and the Orthodox Jewish community”, she added, with the aim of helping unregistered institutions “meet the requirements for registration with Ofsted.
“Where we become aware of unregistered institutions, we inform the DfE so that Ofsted can visit the schools to consider curricular and safeguarding requirements.”
Strictly Orthodox girls predominantly remain in secondary education for longer and often perform well at GCSE.