Around a third of the 22 boys on the roll, aged from 13 to 16, are studying GCSEs in English, maths, physics and geography, which were introduced last year.
But standards were low, “largely because many teachers do not have the skills and knowledge needed to teach pupils at greater depth”, Ofsted reported.
The secular curriculum did not give pupils a “rich learning experience”, with physics the only GCSE science on offer and art and PE limited.
Leaders of the school had an “inflated” view of pupils’ progress, which was not borne out in the boys’ work-books.
Although pupils had good listening and speaking skills in English, they had only limited opportunities to practise writing or read great works of literature, Ofsted said.
Opportunities to learn about Britain’s main religions in greater depth were also limited.
The inspector also reported that the school had failed to notify the local authority about the status of privately fostered pupils. “As a result, the local authority has not been able to carry out the appropriate safeguarding checks on the fosterers, thereby putting these pupils potentially at risk.”
In contrast to the secular programme, the school received praise for Kodesh (Jewish studies), which effectively promoted spiritual and moral development in a “nurturing environment”.
Pupils were “constantly challenged to think and reason and to draw on centuries of interpretation to support their arguments about how to live as a Jew in modern Britain”.