During the previous major phase of Conservative education reform, Michael Gove had one particular target in his sights. Not The Blob – that was merely an obstacle to overcome to achieve his aims – but what George W. Bush famously called “the soft bigotry of low expectations”. As Gove put it in 2013, he was out to destroy:

“…the soft bigotry of low expectations which has governed education for too long by refusing to accept that children from poorer homes can’t be expected to do just as well, to achieve just as highly, as their wealthier peers.”

Then, the measures deployed were two-fold: raise the quality of the curriculum and the rigour of exams, and raise the general standard of schools by introducing competition in the form of free schools and greater freedom through academisation. That process isn’t over – 131 more free schools were approved yesterday – but it has already shown result, as Gove’s successor, Justine Greening, said in a speech in Twickenham today:

“1.8 million more children in good and outstanding schools since 2010, 1.8 million more children getting a better start and a better chance to realise their potential.”

Greening’s speech wasn’t an exercise in resting on laurels, though. The education system is improving, but it still hasn’t reached the stated goal that “We want all our children taught in good and outstanding schools.” (How’s that for a rejection of low expectations?)

The Education Secretary’s job is already complex – she’s battling with an awkward and controversial change to the school funding formula – but she also has to design and then push through the Prime Minister’s personal addition to Gove’s reforms: the provision of new selective schools.

A white paper will be coming out soon, which will provide more detail, but today’s speech gives some insight into how Greening intends to navigate these choppy waters. In keeping with the approach for Free Schools, she wants the move to selection to be the decision of “parents and communities” in each local area. That’s right, and suitably localist, but it’s also politically wise. As Nicky Morgan discovered on academisation, a top-down proposal can spur opposition on the Conservative as well as Labour benches, and be sunk in Westminster. It’s far harder for those MPs who dislike selection to vote down the idea that parents in each area should have the right to decide whether it should be adopted.

Less clear, and more controversial, is how she will address concerns that selection is simply a gift to better-off parents who are able to game the exam system through private tutoring or passing on to their children the general advantage of enjoying a better education themselves. Greening is evidently sensitive to the argument:

“…the new schools that we will create will support young people from every background, not the privileged few. Young people on free schools meals – those eligible for pupil premium. Young people from ordinary working families that are struggling to get by. I want these new schools to work for everyone.”

This sounds nice, but it’s easier said than done. How will selective schools “work for everyone”? Evidently they won’t directly benefit those who don’t pass the selection exam – though a proper and complete reform would also deliver an improvement to the schools which they then attend. Greening appears to mean that she supports measures to give a leg-up to those from less advantaged backgrounds. Or, as she puts it, “to give a priority of places to these children”.

Exactly how that will work will be the next battle. As the Education Secretary notes in her speech, many existing grammar schools already factor in some form of positive discrimination to try to ensure fairness despite background. (Syed Kamall, for example, wrote on this site about how his own alma mater, the Latymer School, has introduced “a modest bias to help candidates from difficult backgrounds”).

The forthcoming debate is a victory for advocates of selection, in some ways. Once people are arguing about how it will be implemented, they have implicitly accepted the idea that it is going to happen. But the devil in the detail will still no doubt be controversial.

The row over the funding formula already illustrates how hard it is to accurately calculate who is privileged in some way and who isn’t, and by how much the misfortune of one should be compensated. Inevitably, some people end up upset. With new grammar schools, there will be vocal opposition that the least well-off are being left behind. If Greening acts to head off that risk, she will instantly upset some of those better off parents who support selection on the assumption that their own children will be selected but who will find themselves discriminated against. Get the balance right, and she will win through – get it wrong, and she could stir up new opponents without finding new supporters.

The trick will be nurturing and shepherding her coalition – ensuring that those she upsets are outnumbered by those she pleases, and that those she helps lend their support for her plan, rather than just falling into silent contentment.