The head of Ofsted has issued a sharp rebuke to schools in England that continue to “off-roll” vulnerable pupils and force others to take “sham qualifications” in order to maximise results and improve league table positions.

The schools watchdog introduced a new inspection framework last year aimed at encouraging schools to move away from a purely results-driven culture and focus instead on a broad, rich curriculum.

However, according to the chief inspector of schools, Amanda Spielman, a minority of schools are continuing to “game” the system, intent on putting their own interests ahead of their pupils’.

The new inspection regime has been criticised by some multi-academy trusts, who have described it as a “middle-class framework for middle-class kids”. They say it penalises schools in disadvantaged areas who may be marked down for running three-year, rather than two-year, GCSE courses for some pupils.

Speaking at the launch of Ofsted’s annual report in London, Spielman warned against a narrowing of the curriculum and said some children – particularly the most disadvantaged – were not being well prepared for adult life because of the limitations of their education.

“We must guard against restricting education excessively,” she said. “Exam results are important but have to reflect real achievement. We should not incentivise apparent success without substance. This doesn’t represent a good education for any child.”

Spielman said Ofsted inspectors recently visited a school where every child was required to take a sports science qualification at GCSE, “whether or not they had any interest in sports science at all”.

“We’ve seen schools requiring almost every child to take a qualification in English for speakers of other languages, even though they were nearly all native English speakers who were also taking English language and literature GCSEs.”

Elsewhere she said schools were cutting back drastically on languages, art, music, drama and humanities. “We mustn’t succumb to the seductive but wrong-headed logic that we help disadvantaged children by turning a blind eye to schools that narrow education in this way, as long as they deliver acceptable grades at the end. Grades are hollow if they don’t reflect a proper education underneath.”

Mary Bousted, the joint general secretary of the National Education Union, blamed Ofsted for creating the conditions where schools felt under pressure to teach to the test. “A new framework may change school behaviours on the surface, but fear-driven change is not the way to embed better practice in schools.”

Spielman, who was delivering her third annual report, said the majority of schools (86%) were good or outstanding, but warned against complacency, highlighting continuing failures, particularly in the provision for children with special educational needs and/or disabilities (Send).

The Ofsted report said there was a lack of coherence and coordination in Send provision, with parents too often encountering “fractures” in assessment and planning. “In these cases, the system is not working well as a whole to make the best decisions and achieve the best outcomes for children and young people,” it said.

Responding to the report, Chris Keates, the acting general secretary of the NASUWT teachers’ union, said Ofsted was right to highlight that in too many cases across the country, Send pupils were being let down by failures in joint working arrangements between schools, local authorities, health and care services.

“While funding pressures are, of course, at the heart of many of these concerns, it is clear that decisions taken in the last 10 years by the government to dismantle the highly effective local joint working arrangements it inherited has wrought lasting damage on the Send system.”

The report says Ofsted continues to be concerned about the number of pupils leaving schools during their GCSE studies, with 20,000 pupils leaving between years 10 and 11. The problem is particularly acute in 340 schools where there have been exceptionally high rates of movement.

Despite improvements, fewer than half (48%) of local authority children’s services are rated good or outstanding. The report notes that such services continue to struggle with “chronic underfunding” and increasing demand.

It also raises concerns about the children’s homes sector, warning that there are not enough children’s homes where they are needed and no joined-up strategy to meet children’s needs.

The report warns that the most concerning provision is hidden from sight. “These areas, like unregistered children’s homes, unregulated provision for care leavers and unregistered and illegal schools, are where children are potentially coming to significant harm as a result of poor commissioning decisions, ill-informed parental choices or simply unsafe and unsuitable conditions for children.”

Spielman also had harsh words for the government, criticising the Department for Education for lack of leadership in the row over LGBT lessons in primary schools.

Children and teachers had to withstand noisy pickets outside a small number of schools, including Anderton Park primary school in Birmingham, where parents and others were protesting against relationships education.

“The children, as well as teachers, had to walk into school past placard-waving protesters and then listen to [a] diatribe blasting through megaphones outside. It was, quite simply, intolerable,” said Spielman.

“And yet, there was no swift condemnation from government and remarkably little from other local and national political leaders. The powerful voices that should have supported the children and the school were largely muted.”

Spielman said headteachers were left feeling isolated. “Where leadership was desperately needed, it was lacking. So we spoke out. We backed the headteachers under fire and we said unequivocally that children should learn about different kinds of family.”

The government is introducing compulsory relationships education for primary schools and compulsory relationships and sex education for secondary schools in England from September.