It is hard to know whether the apparent dip in applications to Jewish primary schools in north-west London, which we revealed last week, is a one-off quirk or of more lasting significance. We simply don’t have enough data to tell.

Of the 14 state-aided Jewish primaries in the borough of Barnet, 11 recorded a decline in demand. Of the three which bucked the trend, one had just a single application more than last year, another two more and a third 11. On the other hand, one school had 60 fewer applications (though still more than three for every place) and another 30 fewer.

While most schools will have no trouble in filling their places, the largest, Sinai, had allocated only 52 of its 90 places on national offers day last month, according to Brent council’s website.

Since then, Sinai may have picked up Jewish pupils unable to find a place at another school closer to home. But if it still has vacancies and there are children in Brent without a place, then Sinai may have to accept children from other faiths.

While Sinai is within reach of Hendon and Edgware, the fall in the immediate Jewish population in Kingsbury and Kenton has raised questions of whether the school is now in the best location. In recent years, it took an “overflow” from Hertfordshire where there were too few Jewish school places but the opening of Yavneh Primary in Borehamwood last September has reduced that potential source of recruits.

The probable explanation behind the fall in applications more generally is that fewer Jewish children outside the Charedi community were born in the relevant year. That is the line coming from the Institute for Jewish Policy Research, which collects demographic data.

The application figures on their own are not conclusive. Here’s why. Let’s  say you have an area with five Jewish schools, each of which can take 50 pupils a year -  250 places in total. There are 400 Jewish children in the local area and three-quarters opt for a Jewish school. Each family can put down four Jewish schools and for argument’s sake, let’s say each family which applies puts four Jewish schools. So overall, the five Jewish schools should receive 1,200 applications between them (300 x 4).

Next year, there are only 1,100 applications. It could be because fewer Jewish children were born that year: or a smaller proportion opt for Jewish schooling: or more parents select a mixture of Jewish and general schools.

What we don’t know is whether the decline in primary applications this year signals a longer-term trend, heralding the end of the post-millennium mini-boom in non-Charedi Jewish births. And if there are fewer children coming into primary schools, there will be fewer applying for Jewish secondary schools in future years.

That may influence the argument over whether the best way to solve the current shortage of secondary school Jewish places in north-west London is to expand the existing schools – as has happened this year, with bulge classes at JCoSS or JFS; or to open a new school altogether, as the backers of the New Jewish High School aim to do.

The key factor is what happens if down the line you end up with over-capacity at Jewish secondary schools. If you don’t mind children from other faiths at a Jewish school – indeed you might think that is a good thing – then there is simply no issue. It is better to have more places than you need than risk a single Jewish child being left without a place at a Jewish school.

On the other hand, if you are one of those who favour an “immersive” Jewish environment (the vogue word for an all-Jewish school), then you may not be so relaxed about the prospect of an additional school.