If we were finding better way to teach then kids scores would improve, but they aren't improving.
- The scores don't effectively measure learning.
- The need to prepare students for tests undermines the ability to try different teaching approaches.
- Scores don't change overall but the distribution of scores change.
- The distribution of scores don't change but the demographics of the students in a given part of the distribution change.
- There are confounding factors such as budget or classroom size.
In my 16 years of education, I saw a consistent 1:1 correlation with learning the material and doing correspondingly well on the tests. That consistency included myself - when I learned the material, I'd ace the test. When I didn't learn it, I failed the test. There wasn't any magical "learned but didn't test well" going on.
Consider anxiety disorders. There’s a crystal clear, fully scientifically proven reason that some can know the material but fail to perform on a test. Think more. It helps.
What do "disorders" have to do with class? At best, being from a lower socio economic class could put you at risk for whichever disorders you have in mind, but they aren't synonymous. At least, not in my mind.
I don't assume such people don't exist. But I'm not buying there are enough people to significantly alter overall student test results. There'd have to be a couple in every class, and I've never encountered one.
As an example: do you consider solving 579×46 quickly a "math problem"? I will solve it (relatively) quickly, since I was thought how to solve that exact problem algorithmicaly.
But if you hadn't thaught that algorithm (you could argue that nowadays we have calculators for this) then it would probably take you a bit longer to derive some form of this algorithm. But it doesn't necessarily imply that you're bad at math, just that you have not practiced this exact task before.
In my experience, doing really well in tests requires more adaption to the tasks of the tests than actual understanding. Most tests are limited on time, and stress does not exactly help you to deal creatively with completely new tasks.
Note that I don't want to say that teaching algorithms is bad. It surely helps to do some basic calculation without having to think much about it. I just want to point out that the tests are often testing a specific understanding of math, and different teaching methods often also differ in their goal of what they want students to learn well.
It's second or third grade material. It's reasonable to expect teachers to teach it and kids to learn it. It's easy to create tests for it.
I don't think that ability necessarily has a great deal in common with understanding mathematics or the ability to do higher level math.
As a result it provides vanishingly poor outcomes which keep the US below the OECD average, in spite of some of the highest per-student spending in the world.
Education is highly politicised, managed by school boards which seem to attract religious kooks and other low-quality authoritarians with eccentric ideas, and which does almost everything it can to discourage good teachers and other suspiciously well-educated and competent individuals from joining or staying in the profession.
Widespread poverty in the US population doesn't help.
Changing how math is taught won't address the essential dysfunctional broken futility of the system as a whole.