Last week the education secretary Justine Greening finally confirmed the worst-kept secret in Westminster: she’s going to change to the law to make sex and relationships education (SRE) compulsory in all state schools.

Currently, different types of schools have different obligations in this regard, and the response to this proposed expansion was generally positive.

There was much agreement because there are nearly as many ideas of how SRE should be approached as there are proponents.

For instance, a charity called Plan International recently suggested that children in England should be taught about the implications of “sexting” and pornography. The CEO said it was important that pupils’ education reflect the realities of the 21st century.

It’s hard to disagree with such sentiment - and a poll commissioned by the charity revealed that most of the public agreed, too.

But at some point, headteachers, teachers and parents have to make choices about prioritising what schools are actually for. School days aren’t that long - around four to six hours of teaching - but external groups endlessly press schools to take on more responsibilities. If schools accepted all these calls, there would be practically no time for serious academic work.

Over the past few years, we’ve heard charities, pressure groups, politicians and commentators call for schools to deal with the following areas (and more): sexual abuse; personal finance; CPR; the importance of hygiene; cooking; coding; reading music; philosophy; British values; extremism; self-sufficiency; activism; public speaking; and collaborative problem-solving.

To attempt to list them like this is not to ridicule them - each of them has merit - but it shows the pressure that schools are under to massively widen the scope of their teaching. And this ignores additional demands for certain subjects - like religious education - to be made a formal part of the EBacc.

It’s hard enough for seasoned politicians to draw a line in the sand and publicly point out that not everything - and not even every important thing - can be taught in schools. It’s even harder for individual schools to do so. They worry about the hostile attention they’ll receive from organised lobby groups - sometimes backed by influential, well-known people - for stating the obvious. Because of this, the education debate can sometimes become detached from reality - where too many people think that too many schools have got too much time on their hands.

But we must be honest about the limited time available and the fact that serious academic work must be the overwhelming priority in the school day - and indeed across a child’s lifetime at school.

‘Schools can’t be responsible for everything’

Fundamentally, it’s down to schools to teach academic work, and it’s down to a mix of parents, charities, churches and other civil society groups to fill in the considerable gaps in a child’s broader education. Schools can’t be responsible for everything.

As a father of four primary-aged girls, I am only too aware of my responsibilities at home. As a head, I see all too often the consequences of families not playing their part in bringing up their children, and the additional burden this places on us in schools, already working at full capacity.

This is not to say that schools have no responsibility for helping with a child’s personal development or the teaching of what we might call “life skills”. Some time is rightly set aside by schools for this - and successful schools provide children with vital, ongoing advice informally through their school lives. There are many, many benefits of extra-curricular activities.

But academic success - which is vital for university, securing a good job and indeed to understand the world around us - is hard-won. While it’s possible to do reasonably well at school by, for example, reading summaries of books on the English literature course, or skillfully reading revision guides for science and maths, the highest performance is only achieved by pupils who immerse themselves in their subject. This takes time.

Some will argue that no choice has to be made - that it’s possible to teach academic work and an array of additional material to help children develop. This is only true to a point. Every time we allocate time, money or staff to do one thing over another there is an opportunity-cost analysis to be undertaken - and we must understand that.

If teachers taught everything from understanding personal finance to avoiding or dealing with pornography, there would be no time for anything else.

Our schools have greater freedoms in how they run themselves than ever before, but there are only so many hours in the day, and only so much money and so many staff available. I think it’s time we had some difficult and honest conversations about what we can realistically ask our schools to do - and that includes whether teaching SRE is, in fact, a good use of our teaching time. Or whether students would be better off if we used the time to teach something else instead.

Mark Lehain is founder and principal of Bedford Free School, and on the advisory Councils of Parents & Teachers for Excellence, and the New Schools Network.  He tweets @lehain

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