I always struggle to understand why people get so hung up on concepts. In Maths exams we get given questions which require answering. Understanding can not be tested in an abstract or any other way which is divorced from that. Understanding is simply inferred from a correctly answered question. It goes without saying that the student needs to know the underlying maths methods but at A level a huge formula book is provided. The true significance of this obvious fact is rarely mentioned in this forum or elsewhere at all. The number of formulas a person really needs to know for each module is very small. The word "concept" does not appear in the spec to my knowledge, nor in exams nor in text books. If concepts were important in isolation then the proofs of the rules of calculus, and finding the leading derivatives from first principles would be in the spec. But they aren't.