Why Maths goes wrong, and where
A child who “cannot do Maths” can almost always do Maths. What has usually happened is that one idea, two or three years back, never landed — and everything stacked on top of it since has been guesswork.
The gap is older than the topic
A Grade 10 student stuck on quadratics is very often a Grade 7 student who never quite believed that a letter can stand for a number. Re-teaching quadratics more loudly does not fix that.
We find it before we teach
The trial assessment is a handful of questions spanning several years of the syllabus, chosen to show exactly where the reasoning stops and the memorised procedure takes over.
Then we rebuild from there
The missing idea is taught properly first, and the topics above it are revisited in order, so this year's syllabus finally has something solid to stand on.