Back in Jr High I took band class and ended up playing the baritone horn. The easiest brass instrument to play and perhaps the heaviest to carry on the school bus - except for the tuba. I liked it, got pretty good at first but after a while it seemed I was no longer improving. The band teacher was first rate, very demanding and very thorough and I was wanting to get better but after a while I dropped out. A few years later I figured out why I wasn't able to play those 1/16 notes or the triples. I had spent years starting a note with a puh instead of a tuh. It works at first but then you're stuck.
At the Jr High level it's hard to hear the difference between the two if you're a teacher listening to a never ending supply of kids playing badly. And I'm sure the teacher never considered the fact that in spite of the 900 times he explained the correct way - i just wasn't getting it.
The same thing happened in High School. Four weeks of swim instruction as part of 10th grade gym class. I was the fastest kid in my class but I never changed my stroke to be in line with what the coach was telling us. I got a B and was outraged enough to pass on an invitation to join the swim team.
I was a hard case as a kid, I'm a much more patient, methodical learner as a 65 year old. I've continually improved my swim technique, I've made myself respectable on the C2 rowing machine and I'm learning pretty good form on the TT bike. I also taught my self to type. Something I couldn't do in 1990.
Why am I telling you all this? Sometimes it's the student, not the teacher.