In 2010 when the Coalition ditched a school performance measure known as contextual value added (CVA), the news barely registered. It may have been designed with good intentions - to avoid unfairly penalising schools in disadvantaged areas by taking into account pupils’ prior attainment and socio-economic background. But even those who CVA was supposed to benefit struggled to understand it.

And yet its passing is significant for anyone who wants to understand the attitude of Conservative ministers toward schooling disadvantaged children, an attitude shared by Ofsted’s current leadership.

They want these children to do as well as their most privileged peers. And for that to happen, they believe that the emphasis should be on fairness to the pupil, not the school. Why waste energy on a measure like CVA, showing that schools with low results in “challenging” areas have done OK, all things considered? Why waste time on something that takes pressure off teachers, when pupils leave with actual grades that will disadvantage them for life?

It is the same laudable logic that calls for a focus on the young people in schools, not the adults; that demands the “100 per cent school”, where all succeed, whatever their background, and that rejects the “soft bigotry of low expectations”. But it is a logic that can blind policymakers to uncomfortable truths that face anyone who teaches in disadvantaged areas today. Home life does make a difference to pupil performance, and many children lag behind their peers in vocabulary and cognitive development years before they enter the classroom.

Schools should, and do, try to overcome these problems. It is not acceptable for teachers to excuse low exam results for disadvantaged pupils with a,“Well, what do you expect?”

But evidence suggests that they are facing a daunting task. There are many good schools in England, there are lots of good schools with many disadvantaged pupils, and there are plenty of these schools in the North, as the rejected CVA reveals. However, there are very few, if any, schools so good that they can eliminate the impact of the most deprived backgrounds on relative educational achievement.

That, however, is exactly what ministers and Ofsted seem to expect when they decry a supposed North-South divide in school standards. It is a “divide” that they appear to believe they can solve with a few stern words and some academy takeovers. When that fails to make a difference, ministers will face a choice. They can try to get to tackle the social problems in deprived areas, or they can further increase pressure on schools.

Recent history has shown us where the latter choice can take us, with schools incentivised to game league tables and to avoid admitting the very pupils who most need help.

Ministers and Ofsted cite the example of London to anyone who says that poor results can’t improve relative to the rest of the country. But research suggests that pupil background was the factor behind the capital’s remarkable turnaround.

And even if it wasn’t, the London Challenge, which had a positive, collaborative approach, was a world away from the lazy generalisations about a North-South divide in school quality that are deployed today. Everyone wants disadvantaged children to achieve more. But sweeping condemnations of teachers working in some of the poorest parts of our country are unlikely to help.

This is an article from the 29 January edition of TES. This week’s TES magazine is available in all good newsagents. To download the digital edition, Android users can click here and iOS users can click here

Want to keep up with the latest education news and opinion? Follow TES on Twitter and like TES on Facebook