You'd think it's the reading of the staff or the positioning of your fingers. Well, those are all pretty hard. (I should have learned it as a child. Instead I played the brat and lost my chance. And my mom was never very much adept of second chances)
But, yeah, those are all hard things to learn. However those are hard things for everyone one.
It's hard having to understand that DÓ RÉ MI FÁ SOL LÁ SI are now called C D E F G A B
Bemol and sustenido are flat or sharp, and I don't even know which one is which.
See, maybe if you are a musician, those transfers are easier to you. But I am not. I am just a girl who likes to sing her favorite songs and who would like to play them in the guitar, just for fun.
Makes me think of my ELL students trying to learn science, math, social studies in English. They are not scientists or mathematicians, or historians or geographers. They are just normal children trying to survive in school.
Just like you and me once were.
And they have to relearn school language in English.
If you want to understand how your ELL students feel in your class, trying learning music in Russian or something.