The issue of off-rolling is becoming more prevalent by the day.

From being a term that many in education circles had not even heard of just a few years ago, it is now is a hot topic in the sector.

Everyone seems to agree that schools off-rolling pupils from their books in order to boost league table scores is a problem, but what exactly does the term mean?

Quick read: Police chiefs link off-rolling to knife crime

Quick read: Spielman says Ofsted has identified off-rolling at three schools

Comment: 'There's a difference between off-rolling and exclusions'

With heads now seeking talks with Ofsted over the issue, here is everything you need to know.

Who is talking about off-rolling?

Pretty much everyone in education. Ofsted has promised to tackle it through inspection reports and has already identified it as taking place in three schools.

The government’s Timpson Exclusion Review will also address the issue.

Education commentators, government advisers, school leaders and teachers all agree that this is a major problem.

And this week the topic spilled out beyond the education sector when police chiefs and the mayor of London called for the practice to be stopped in a letter suggesting that a "broken" school exclusion system was driving up knife crime. This assertion was roundly rejected by voices across the education sector.

So, what is off-rolling?

There is no legal definition of the practice. However, Ofsted has come up with one for its inspectors to use. Ofsted defines off-rolling as: “The practice of removing a pupil from the school roll without a formal, permanent exclusion or by encouraging a parent to remove their child from the school roll, when the removal is primarily in the interests of the school rather than in the best interests of the pupil.”

Is this different to permanent exclusion?

Yes, and the two issues being conflated is one of the biggest concerns among school leaders.

Ofsted itself has been clear that it supports the right of schools to permanently exclude pupils. Off-rolling is understood to be a way in which schools lose pupils without having to exclude them formally.

The two issues can get lumped together, though, when people criticise the school system for not being inclusive enough. This happened a week ago when police chiefs and the mayor of London, Sadiq Khan, called for an end to what they described as “off-rolling exclusions”.

So will Ofsted fail off-rolling schools?

The answer to this comes in three parts. Yes, it will, yes it has done – but not always.

Ofsted’s new inspection framework handbook says that schools found to be off-rolling are likely to get an "inadequate" judgement for leadership and management and therefore an overall "inadequate" judgement, too.

Not only this but Ofsted has already started identifying off-rolling in its inspection reports.

Tes has revealed reports for Harrop Fold School – which featured in TV’s Educating Greater Manchester – and Shenley Academy, in Birmingham. Both were judged to be "inadequate" and placed in special measures. However, a report for Discovery Academy, in Stoke-on-Trent, referred to off-rolling but the school was judged to be "good" overall.

How can a school that is off-rollling be 'good'?

It is a fair question. The inspectorate judged the leadership and management of the school to "require improvement" while finding the overall education provided to be "good" – including the teaching and learning, and the outcomes achieved by pupils.

The other point to make is that this school was inspected under the current framework while the tougher stance Ofsted is set to take on off-rolling will come in from September.

Given what Ofsted has said about the new framework, it seems reasonable to assume that the school would have been judged more harshly with an "inadequate" grade, had this evidence been found after September

But this does leave Ofsted facing criticism that it has sent out a mixed signal about off-rolling and how serious a problem it is.

Are heads happy with the crackdown on off-rolling?

Yes, in principle, but there are concerns that the Discovery Academy case highlights.

There is universal condemnation of any school that removes pupils, leaving them to drop out of the school system altogether, be home educated or end up in unregistered provision, because it cares more about its exam results.

Geoff Barton, the general secretary of the Association of School and College Leaders, described the practice as  “unethical, inappropriate and beyond repugnant”.

But the heads' union has also warned that school leaders need a clearer understanding of what Ofsted means when it talks about off-rolling.

In Discovery’s case, the school had moved pupils into alternative provision earlier in their secondary education but did not take them off its rolls until Year 11.

ASCL’s director of policy, Julie McCullough, has warned that currently Ofsted’s definition of off-rolling pits the interests of the school against the interests of the pupil, when, in fact, in some cases a decision to move a pupil could be in the interest of both.