Can you spot the factor missing from this BBC report

The BBC manage to report on a shortage of school places without mentioning the main factor causing this shortage:

'School places under real strain, spending watchdog warns 

 A quarter of a million extra school places will be needed in England by autumn 2014 to meet rising demand, the National Audit Office is warning.

The spending watchdog said one in five primary schools in England was full or near capacity and there were signs of "real strain" on places.

The demand for places has been driven by England's birth rate rising quicker than at any time since the 1950s.'

A long report that manages not to mention immigration at all.

Here's some context from The Telegraph last October:

 'New figures show that the number of immigrants having babies has doubled since 2001, largely driven by an influx of Polish, Pakistani and Indian mothers.

This has been the main reason behind an increase in the overall UK birth rate to its highest level in decades, with 808,000 births last year, compared with 670,000 in 2001.

The spike in the birth rate is biggest in London, where six in ten babies are now born to immigrants each year.

Figures from the Office of National Statistics shows the highest increase in births has been in the Polish community, since the country was admitted to the European Union.

In 2001, fewer than 2,000 babies were born in Britain to Polish mothers.

This has now increased by at least eleven-fold to 23,000 last year, making Poland the top nationality for creating second-generation immigrants to the UK.

Women from Pakistan, India, Bangladesh, Nigeria, Somalia, Germany, South Africa, Lithuania and China have the next highest number of babies.

Birth to UK mothers have also risen, with British-born women have an average of 1.89 children.

However, they are not keeping pace with the births of children to foreign women in the UK, who are giving birth to an average of 2.28 children.

The proportion of foreign-born women of child-bearing age living in the UK has increased from 14 per cent to 18 per cent since 2007, giving them a substantial impact on the overall number of births.'

So why no mention of immigration in the BBC's report?