The British education system’s inconsistent approach towards racist incidents within schools is potentially putting children of colour at a disadvantage for the rest of their lives, the former children’s commissioner for England has warned.

Anne Longfield also called on the government to review its education policies, with a particular focus on children who are excluded from schools.

Through interviews, freedom of information requests and extensive research, the Guardian found huge disparities between how schools dealt with and recorded racist incidents, due to a failure by central government to issue proper guidance.

Longfield urged ministers to give schools increased clarity on how to tackle racist incidents, and in some cases systemic racism within their institutions.

“The response from schools is very inconsistent, some will feel much more confident about it than others, and I think what this comes down to at the end is about a system,” she said.

“So some of it, of course, is about schools policy, but it might also be about policy from the Department for Education [DfE]. It’s all about joined-up thinking.

“I don’t have any reassurance that there’s consistency in dealing with [racism] and what we see happening in terms of the level of exclusions in some schools.”

In May 2019 the then education secretary, Damian Hinds, called on headteachers in England to expel fewer pupils, as an independent study – the Timpson review – revealed almost eight out of 10 permanently excluded children came from vulnerable backgrounds.

The long-awaited analysis of exclusions in England, carried out by Edward Timpson, a former minister for children and families at the DfE, found 78% of expelled pupils either had special educational needs (SEN), were eligible for free school meals (FSM) or were “in need”.

The Guardian has since found that exclusion rates for black Caribbean students in British schools are up to six times higher than those of their white peers in some local authorities.

Longfield said this highlighted that some schools were more capable of meeting the behavioural needs of certain children, while others were consistently failing due to their rigid school structure.

She said the Timpson review “highlighted that there were two aspects of a child being excluded. One was the child and how the child was behaving and the other was the characteristics of the school. What became clear was that about 90% of the exclusions were actually taking place in 10% of schools.”

But Longfield said that despite ministers accepting there was an urgent need for reform, with Hinds confirming the government would act on the review’s recommendation that schools should be made accountable for the pupils they permanently exclude, in reality little had changed.

“So I’ve been disappointed it hasn’t been followed up,” she said. “The government is continuing with its expansion of alternative provision and I accept that there are times when children have to be out of school but I would like that alternative provision to be focused on how you keep children in school.”

In September an Institute of Race Relations (IRR) report focusing on London said government responses to inner-city youth rebellions and moral panics over serious youth violence and knife crime had led to black pupils disproportionately being sent to pupil referral units (PRU) and alternative provision (AP).

The IRR report noted that 89% of children in detention in 2017-18 reported having been excluded from school, according to the HM chief inspector of prisons for England and Wales.

Last June the government announced an additional £750 per pupil to support students leaving AP to transition into education or training, but even with the extra funding school leaders said one in four students would still not have anywhere to go in September.

Longfield said the situation with exclusions and APs was just one example of how BAME children were being put at a disadvantage. She also cited the disproportional number of black children in custody and also on remand, with the proportion of children who received a youth caution or sentence who were BAME almost doubling since 2010, from 14% to 27% in 2018.

“Certainly there are inequalities within the school system, and there’s a school system that isn’t yet geared up to be able to either reflect the lives of those children, or indeed support those children,” she said.

“If you ask any of those kids [in custody] about their schooling, they will nearly all tell you they were excluded from school. After they’ve been excluded the first time, put a whole package of support around that child. It’s just obvious.”

Longfield also called for data on racist incidents within schools to be routinely collected, allowing public bodies and ministers to get a clear picture of what is happening within the UK education system. Without central data collection, she said, it would remain a challenge to tackle systemic racism due to a lack of understanding.

“We need to ensure that all children when they’re in the classroom feel safe, that they feeling that supportive environment, and that they know others have got their back- that it will be taken seriously,” she said.