Sweeping education reforms appear to be fuelling inequality in the schools system, according to a major analysis that shows high-performing and improving schools are accepting fewer children from poor backgrounds.

In a stark assessment of the impact of controversial measures introduced since 2010, the study warns that an original pledge to set schools free and give them more power has actually led to a system that is causing high levels of stress among teachers.

It finds the system is now pushing schools and their heads to prioritise “the interests of the school over the interests of groups of, usually more vulnerable, children”. Some schools were found to be engaged in “aggressive marketing campaigns and ‘cream skimming’ aimed at recruiting particular types of students”.

The findings form part of a state-of-the-nation study of England’s education system, drawn up by academics at the UCL Institute of Education over four years, which will be published on Tuesday. It includes the examination of Ofsted data over a decade, a statistical analysis of the impact of multi-academy trusts (MATs), 47 detailed school case studies and a survey of almost 700 school leaders.

The reforms were largely implemented under the coalition government and championed by Michael Gove as education secretary. A plan to force all English schools to become academies was abandoned in 2016 after a backlash among Tory MPs.

The study concludes that any new autonomy handed to schools had been “more than balanced” by testing and inspections that had ensured the state remains in control from a distance. The drive to turn schools into academies, the key part of reforms since 2010, is described as “uneven and often fraught”.

There is also worrying evidence of schools improving or keeping their high status by shunning children who qualify for free school meals, whose parents receive state help. “Our analysis of national Ofsted data for the periods 2005-10 and 2010-15 showed a relationship between inspection grades and the changing socioeconomic composition of a school’s student body,” say the authors, Toby Greany and Rob Higham.

“Schools that sustained or improved their judgment to ‘outstanding’ in the 2010-15 period saw, on average, a reduction in the percentage of students eligible for free school meals (FSM), while schools retaining or being downgraded to a ‘requires improvement’ and ‘inadequate’ judgment saw, on average, an increase in FSM eligibility.”

The study admits it cannot say conclusively why better-performing and improving schools have admitted fewer poorer students.

The analysis says that there are signs of challenging pupils accumulating in underachieving schools. “While higher-status schools were seen to be benefiting [from reforms since 2010] in terms of new opportunities and resources as a result of policy reform, the lower-status schools we visited faced a concentration of challenges often including under-subscription, higher mobility and disproportionate numbers of disadvantaged, migrant and hard to place children,” the study concludes.

“Two-thirds (66%) of respondents [to a survey of school leaders] agreed that inequalities between schools are becoming wider as a result of current government policy.”

The study amounts to a stark assessment of sweeping education reforms introduced in the past eight years, as part of an attempt to build a “self-improving school-led system (SISS)”. Key measures include forcing schools to become academies, the promotion of multi-academy trusts (MATs) and the rolling back of local authorities from education.

Ministers said the reforms would “dismantle the apparatus of central control and bureaucratic compliance” by handing power to schools. However, analysis by the academics shows there is no positive impact from MAT status for pupils in either primary or secondary academies when compared to pupils in similar standalone academies. For secondary schools, there was no statistically significant benefit for students when compared to all other schools.

It looked at data from 2009 to 2015, examining average performance and progress of children at primary school, including in reading, writing and maths. For secondary school pupils, it examined the proportion of students achieving at least 5 GCSEs or equivalent qualifications at A*-C including English and maths, as well as their progress in English and maths.

School leaders deemed to be leading the way in the new system are being handed new opportunities and power, it finds. However, it adds that they are faced with “conflicting and unreasonable demands” from government, while being treated with suspicion by less favoured schools. The study warns of the power that the new system can hand to “charismatic, authoritarian leaders”.

It warns that the system in which the involvement of councils has been stripped back, with fellow schools encouraged to help their struggling counterparts, is actually seeing the creation of a market for advice – with schools charging for their expertise on how to improve.

A Department for Education spokesperson said: “Thanks to our reforms and the hard work of teachers, the vast majority of pupils are in a good or outstanding school, 1.9 million more than in 2010, and an increase from 66% to 86% over that time.

“And thanks to our reforms schools that aren’t delivering for young people are being turned around, with 65 per cent of schools made into a sponsored academy seeing improvement from inadequate to good or outstanding. But there is always more to do, which is why we are investing £23bn by 2020 to create more good school places and we are targeting £72m at the areas that need it most to help improve prospects and opportunities for some of the most disadvantaged young people.”