We know there is an issue - the data makes this clear. But the question is, why is this happening?
One suggestion is that the GCSE Maths and English curricula are expecting too much from pupils.
In her Radio 4 interview, Ms Duffy said that "on maths specifically, we think the current GCSE is far too big and it includes knowledge that isn't required".
"For example, you have to memorise the exact values of trigonometry - and that's something we're not even asking A-level students to do," she said.
For high-achieving pupils in England, Maths is a success story. The country performs well in international league tables for the subject, and more pupils than before are going on to study Maths at A-level.
But Ms Duffy adds: "We also have to expect that at the other end there's more work that we need to do. It can't be that we have a third of students who aren't getting the basic maths skills that they need at 16."
