I teach lawn bowls and am a qualified Scottish coach. I helped write the coaching manual. I have seen all abilities and levels.
The same factors apply. The more natural talent the easier it is to progress. I have seen people progress up through the levels in a few weeks and others stay on level one for years. The teaching methods are the same for all but natural aptitude and ability cannot be taught.
Music theory and songwriting techniques are all very well. However if the pupil has little ear or natural feel then the end results are predictable. THEY WILL GET NOWHERE FAST.