What are schools and education for? I ask because, today, the answer is no longer clear. I believe that the core mission of a school should be the transmission of knowledge and cultivation of pupils’ intellectual curiosity. Yet I fear my view may now be in the minority.

In recent years, education has been transformed into an instrument of public policy by successive governments - a means of achieving objectives that are entirely external to learning. Today, both left and right wings seem to agree that education should be about promoting social mobility, even if some people on the left prefer the term “social justice”. To quote schools minister Nick Gibb in a recent speech delivered to the Sutton Trust, “A welcome consensus has begun to emerge that schools must be engines of social mobility.”

Hardly a day goes by without some politician or economist making a statement about how our schools must better prepare pupils for the workplace. Increasingly, schools are judged not just on exam results, but the number and type of universities their pupils go to. When Ofsted visits a school, we are now expected to have detailed figures, not only on university destinations, but even the jobs they go on to.

This process is happening because schools are increasingly held responsible for social mobility - or the lack of it.

I believe education cannot and should not be thought of as an engine for social mobility. To look to it as such places an undue burden on schools. And I would go even further: it degrades education.

The transformation of education into a vehicle for achieving policy objectives means that it is rarely appreciated as something valuable in its own right. That policymakers confuse education with training and preparation for a career is regrettable. That a significant section of teachers have embraced this backwards agenda is heartbreaking.

‘Philistine’ approach

Prime minister Theresa May’s support for new grammar schools exemplifies the confusion about the role of schools. I believe grammar schools are neither the cause of, nor the solution to, our educational crisis, but what the PM had to say about them is illuminating.

Rather than premise her argument with the traditional strength of a grammar school - a high-quality classical, liberal, rounded education for its own sake - she chose the philistine route. She argued for more selective schools on the basis that they “must deliver social mobility as part of a vision that works for everyone, not just the privileged few”. She is wrong on two counts.

Firstly, it wasn’t grammar schools in the 1950s and 60s that allowed working-class kids to get jobs - it was industrial growth and the expansion of the economy. These children stopped acquiring decent jobs in the 1970s, 1980s and 1990s, not because of “bog-standard comps”, but because politicians failed to deal with structural problems in the economy.

Let’s focus on expanding intellectual horizons, not job prospects

The expansion of white-collar employment had stagnated. Hence, if you want to help disadvantaged young people get good jobs, the best way to do so is to fix the economy rather than expect schools to step in and solve a non-educational problem.

The more such non-educational imperatives are imported into education, the more disorientated teachers and schools become as to their core mission. Social mobility and social justice might be noble goals, but when schools are expected to deliver them, the consequences for education are entirely bad.

One of the principal characteristics of education should be a lack of interest in any ulterior purpose. That does not mean that it is uninterested in developments affecting children and society. It means that it regards transmitting the cultural and intellectual achievements to children as its defining mission. In short, schools should be centres of knowledge, not sites of social engineering. As teachers, our core mission should be knowledge transmission, not social mobility.

The second mistake the PM makes when expecting schools to deliver social mobility is that she fails to grasp the great paradox of education, which is that schools are of more benefit to society when we afford them the greatest autonomy and insulation from the wider concerns of society. That Theresa May is arguing for grammar schools primarily on the basis of social mobility shows exactly how far we have departed from a culture that values academic knowledge for its own sake.

The worth of education

By placing social mobility at the heart of education, all of the major parties reduce academic subjects to skills that might aid employability. For those of us who still value the intrinsic worth of education, we need to remind politicians and fellow educators that it is a dangerous assumption to see social mobility as the objective of education rather than an informal by-product.

It might sound cold-hearted to say so, but the politics of social justice and social mobility should be left outside the school gate. If you want to fight for them, join a political party, but don’t confuse such noble goals with teaching. This is a political question to be resolved in the realms of politics, not education.

As social mobility becomes the moral purpose of education rather than a by-product, education becomes skewed and distorted. Schools will increasingly focus on ensuring the best ways for students to improve their employability and earning potential rather than their minds. The consequence being that the intellectual substance and rigour of subject knowledge becomes increasingly subordinate to skills and employability.

That is a problem we should challenge by opening up a debate. We should be allowed to focus on expanding our students’ intellectual horizons rather than their job prospects.

The right-wing see the point of education as pushing the aspirational minority up the social ladder, hence their support for grammar schools. The left see the point of education as pushing a lot of people up the social ladder, hence their support for comprehensives. Both miss the point of education. It is about us as teachers conveying the seriousness of our subject and trying our best to encourage every pupil towards the joy of scholarship. What happens after they leave school is a political, social, economic and personal question, not an educational one.

Kevin Rooney is chairing a debate at this weekend’s Battle of Ideas, London. He is an author and head of social science at Queen’s School, Bushey