I haven't written music specifically for youth/education, but I've noticed that in that field, many composers will characterize the difficulty levels of their pieces as "grade 3," "grade 4," etc.
Are there lists online with specifics for each "grade" standard?
How does one quantify difficulty level when there are so many factors?
(If there are ensemble-specific lists, I'm primarily interested in finding out the standards for string ensemble music -- and music for solo instrumentalists.)
Thank you.