Sorry GrannyRose I meant to come back to this, and obviously didn't.
my line of work I come across a lot of adults who have very poor maths skills. While some of this is undoubtedly down to other factors, the quality of the teaching they have received during their 12 years in compulsory education must be at least partly to blame for their poor achievement in maths.
I taught maths for decades, I had successes, I had failures. If one teaches Adult Ed Reading and Basic Numeracy, obviously these are 100% folk who've missed out in some way. To then make sweeping generalisations about approximately 900k pupils in each school year based on a minute sample is not really mathematically sound.
While on the subject of statistics, my experience in sec schools (Y7-11) was that attendance was almost always 100% in top Maths sets, but almost never 100% in bottom sets.