'Outstanding'
Inspectors visited Al Mizan primary school and the East London Academy and Jamiatul Ummah - both secondary schools - this week.
Al Mizan and the East London Academy are both independent schools for Muslim boys run by the East London Mosque Trust.
They teach their pupils, who are predominantly from families of Bangladeshi origin, to memorise the Koran and charge fees of £3,000 a year.
Both schools were rated as providing a "good" quality of education and teaching during their last inspections in 2011 and both were rated "outstanding" for students' spiritual, moral, social and cultural development.
Jamiatul Ummah, also for boys only, received an "outstanding" rating for quality of education and provision for students' spiritual, moral, social and cultural development during its last inspection in 2011.
Pupils were found to have "sound knowledge of the multi-faith nature of British society".
None of the schools has commented so far.
The Department for Education said: "Ofsted inspections are routinely conducted at both independent and maintained schools. It would be wrong to comment on individual inspections until findings are published."
These inspections were not part of the 40 no-notice inspections Ofsted announced last month, which stemmed from concern over standards.