After I graduated and whilst maths GCSE’s actually contained and required a good understanding of maths, I used to teach maths and physics part time. Unconventional I used to teach as part of the curriculum Log, Ln, Sine, Cosine and tangents from first principles. One of the biggest improvements in grades was accomplished by going back to basics and getting students to calculate a Log from tables, for example and explaining how they were derived. Why? Well when you understand the principles, and get a feel for what the answer should be, you recognise silly mistakes of hitting the wrong key on your calculator.
About 6 years ago I went down to the institute of Physics in London and did the exam science teachers had to do to get a grant to become a Physics / science teacher (When the government was trying to encourage science teachers) Now, the room was fully a recently graduated Physicists, so I felt rather daunted. I’d only done a Physics A level about 40 years before them. We were broken into groups and took three different tests, one of which was an exam. Two groups had taken the exam before it was my term, and they all came out with long faces concerned at how hard it was. I nearly got back on the train and headed home without taking it. Anyway, I did, and to my surprise it was simple. It was only pitched at what I used to consider O level standard. I achieved 100% in the test, whilst many of the recently graduated in Physics failed. It was a very sobering experience about how far standards in education have dropped in the last 30 years.