There’s an interesting development in Croydon, my scenic home town. The south London borough is fully comprehensive: it has no academically selective state schools (“grammar schools“). Since 1998, it has also been forbidden for new grammars to be opened anywhere in the country, except as replacements for closing ones. But Croydon council has an interesting idea.

Tim Pollard, the councillor in charge of schools, has written about a new school site that the borough is opening. The council want an existing school to run the site, in Norwood, as an annex. If the “parent” school were a grammar, the new half-a-school could be too.

…we took the decision yesterday to open up the competition to run this school to all types of secondary school, not just community-style comprehensive schools. The criteria the new provider needs to meet are that it should be a Good or Outstanding school in its OFSTED rating, that it should have well above average GCSE and A-level results and that it must be able to demonstrate that it can apply its admissions criteria appropriately and be in a position to receive funding from the Government as it expands.

So does that mean it could be a Grammar School? Yes, it could.

In Croydon we converted our last grammar schools into comprehensives many decades ago, in line with what was then government thinking. Our neighbours in Sutton, Bromley and Kent, on the other hand, resisted the intense pressure then put on education authorities to follow suit and kept their selective schools. Those schools, including Wallington Boys & Girls, Wilsons and Newstead Woods, are now amongst the most popular choices for Croydon parents who seek the best standard of education for their children. They are heavily oversubscribed, with many more children passing the exams than can possibly be accommodated.

It will be worth watching this unfold. “Satellite” schools and “annex” sites may be a loophole for establishing new grammar schools. Kent council, which is fully selective, will open a grammar school annex in Sevenoaks. But selection is firmly embedded there.

A Croydon grammar annex would be a bigger step – it would both mean a grammar crossing a borough border and introducing selectivity into a new area. This is all early on, but if Croydon gets this through, it could open up grammars once again as a national issue.

Here is why.

This is a map of Croydon. The green blob is the proposed site for the school. Each of the map polygons is something called an MSOA – a middle layer super output area.

In Croydon, each one has between about 50 and 150 state-educated 16 year-olds (adding up to a total of about 4,000). I have coloured each MSOA blob according to how many 16 year-olds in each one went to a selective state school in 2010-11.

The lightest grey, the colour which dominates, marks areas with five or fewer children in grammars. I cannot be more precise for data protection reasons, but they are, broadly speaking, areas with between zero and three per cent grammar attendance. (Click on the blobs to see local information.)

The dark blue at the bottom left is the wealthy bit of Purley, where 36 of the 107 state-educated children go to grammars. There are two other darker blobs with more than ten grammar school educated 16-year-olds, which have 12 and 17 pupils respectively.

To open a selective satellite school, the annex needs to be plausibly part of the same school. Specifically, the DfE says: “Any school that wants to open a new satellite site would have to ensure that it is drawing from the same demographic population as the school itself.”

If you were to persuade a Sutton grammar to open a satellite site in Purley, that might be pretty easy. They all draw from the area, so children living near to the annex could attend the school (if they passed the test) without breaching the spirit of the law.

If a grammar annex were to open in Norwood, it would be more problematic. It might need to be on the basis that it took few Norwood children. That is because there are so few children from north Croydon who currently go to the nearby grammar schools.

That does not, however, appear to be what the councillor has in mind. He clearly wants more selection in his borough.

If a grammar annex were allowed to open in Norwood, and to recruit from Norwood, on the basis that it already takes some children from the area (perhaps just one per cohort) that would be a big step. It would allow a new expansion of the grammars.

Why? Because if a grammar school can set up new sites and recruit in any neighbourhood from which it currently draws any non-zero number of pupils, it means “satellite” grammar schools sites could potentially be opened in 41 per cent of all MSOAs in England.

My map could be unfair: it might be that Sutton grammars get large numbers of unsuccessful applicants from north Croydon. It remains to be seen if the local grammars would even want to start up a Croydon branch. And the DfE might just kill this off.

I expect that this idea will come to nought. But do watch it. If Croydon is allowed to set up a grammar annex that served Norwood, a “franchising” system could become a model by which the expansion of grammars become a national issue once again.

p.s. More prosaically, this Tory councillor does not sound keen on the “free schools” policy, by which private groups run publicly funded schools. He certainly thinks a four form entry school (c. 120 children per cohort) is not economical if it does not have LA support.

New schools must now be either Academies or Free Schools, which means that they receive funding direct from the government and local councils have little say in how they are run.

This gives the schools greater freedom, but it also means that they must be able to be fully self-financing, with no opportunity for subsidy from the council. The administrative overheads that they need to support themselves mean that, in strictly practical terms, a new four-form-entry (FE) school will now struggle to be viable.

Also, do note the following two points, which are often missed. London’s lack of school places problem is coming, in part, from the recession. People are not leaving the city as they once did. Also note his concern that there’s a real problem with viable school sites in the city.

So why are there more children now? It is partly down to population growth in London and partly down to the effect of the recession, with parents unable to move house as their families grow. What is particularly striking is that the majority of the pressure on places is in the parts of the borough where building is most dense and there is least land available to build new schools or expand existing ones.