Well "wildly wrong" might be a tad too strong, however a crucial part of my hypothesis was indeed wrong, and this has led to failures on my part.
My original hypothesis stated that:
"...my learners were struggling to acquire and retain their basic facts, and other maths knowledge." This is still true, and I still believe this is the problem.
However, the issue with this hypothesis was that first I had attributed the "struggle" to the learner's ability instead of my own (DERP!). It seems so obvious in retrospect, however at the time I had not considered that I myself might be the problem. It is possible of course that my learners have an issue acquiring and retaining basic facts, however a more realistic and far more likely situation is that the "struggle" I talked about, is really attributed to my ability to teach basic facts.
My new hypothesis is the basic idea that if can teach basic facts better so that my learners acquire and retain them, then I will see a greater improvement in higher stages of maths.