At my school, there is a consistent quantity of stuff to learn. That is the same for virtually every test for the same rank. There are a few differences based on age group, but for the most part you are expected to know the requirements on the test. All kids purple belts need to know Basic Forms 1-3, Kicks 1-5, Jumping Kicks 1-3, and Punch Defense 1-5. If you don't know these things, you wait to test until you do know them. However, how well you do those things is where the "progress" comes in. Our basic form (KIbon #1) is essentially just down blocks, punches, and simple turns and steps. For a 4-year-old yellow belt who's been training for 8 months, it may be that simply moving in the right direction is enough to pass, even if half the time they turn wrong or end up on the wrong hand. Whereas older students we'll expect to know at least the basic movements to 100% accuracy. They may not have the best stances or techniques yet, but they at least have some semblance of what the stances and techniques are supposed to look like, and they should be able to execute the steps and turns properly. Let's say a student comes in, and they consistently learn the requirements, and they consistently improve. However, that improvement is very small steps over a long period of time. Let's say the average time to get 4th Dan is 12 years. It could be 3 years for 1st Dan, another 2 for 2nd, 3 for 3rd, and 4 for 4th - longer than the minimum requirements, but a typical progression. This student has been training for 20 years. They've learned all the forms and other testing requirements for 4th dan. But their coordination isn't there. Their stances are still only 90% the definition of a proper stance. Their movements are stiff and disjointed. They never learned how to do their techniques with rhythm or flow. If you were to take your average blue belt (maybe 1.5 years of training) and this guy, have them practice in street clothes (no belts), people would look at them and assume they're peers. That they are a similar level with a similar amount of training. He's made personal progress, but he started way behind in coordination, and the progress was slow. If this student becomes a teacher, he may be able to teach better than he can do. But if he never figured out how to do a lot of the stuff properly, then he probably can't teach how to do it properly. It could simply be that his teaching won't be very effective. It could even be that he teaches the wrong way to do things, because the right way is something he never quite caught onto. Should this student continue to be promoted to higher levels of black belt? Especially considering that the higher you go, the more influence you have? Or at some point should the Master say "you need to be able to meet these metrics for height, speed, proper stances, and so on before you can get promoted."