The BBC's John Cranston: "Nothing about Summerhill School could be termed conventional"

Summerhill School in Suffolk, where children are treated by teachers as equals and can choose whether or not to attend lessons, has been told by the Office for Standards in Education (Ofsted) that it is "not providing an adequate education for its pupils".

The government is expected to issue an ultimatum to the independent boarding school that it must improve standards over the next six months or close its doors.

Although Summerhill is a fee-paying independent school, it is required by law to register with the Department for Education. Ministers have the power to strike a school off this list, making it illegal for it to continue providing lessons for children.

Ofsted's highly critical report focuses on the school's policy of allowing pupils to choose whether or not to attend lessons. It says this has led to some pupils not attending maths lessons for two years.

"Those willing to work achieve satisfactory or even good standards, while the rest are allowed to drift and fall behind," says the report.

Zoe Redhead: "We're being judged against a system that we're not actually trying to keep up with"

"This amounts to an abrogation of educational responsibility and a failure of management and leadership.

"The school has drifted into confusing educational freedom with the negative right not to be taught. As a result, many pupils have been allowed to mistake the pursuit of idleness for the exercise of personal liberty."

Pupils are described as "well-behaved and courteous, if often foul-mouthed".

Summerhill's headteacher, Zoe Redhead, complained that the school was not being treated fairly.

"We're being judged against a system that we're not actually trying to keep up with," she said.

"If Summerhill's going to to be inspected, it should be inspected by people who understand its philosophy and where we are trying to go."

Zoe Redhead: "You can survive without two years of maths"

The report also expresses concern about the school's policy of providing unisex toilets, contrary to social services guidelines, and the quality of its dormitory and hygiene arrangements.

In addition, it notes that one member of staff has not been the subject of background checks.

Founded in 1921 by Ms Redhead's father, AS Neill, Summerhill has been built on principles of allowing children greater independence over how they learn.

The school says that it intends to "create a happier childhood by removing fear and coercion by adults".

Each week, a meeting of pupils and staff decides on the running of the school, with adults and children each having a single vote. This governs such matters as bed times and behaviour rules for the 60-plus pupils, who are between the ages of six and 16.

The Department for Education is keen to emphasise that any criticisms of the school do not represent a judgement about progressive education or any style of teaching, but are part of its obligation to set and monitor standards.