As a band director choosing music for my ensembles, I have found it very confusing to understand the Band Grading System and what it means. Part of the problem is the inconsistency between Publishers, who use different grading systems and terms.
Here in Sydney, most directors seem to use the Grade 1 - 6 system. I recently discovered Belwin (Alfreds) have a good summary on their website. While this may not represent the thinking of each publisher, it is a very good starting point to understand the ranges written for and rhythmic complexity.
A big thank you to Belwin for providing this resource and making Grading a little more transparent.
I also found this useful guide. While a bit messy, (it's obviously a scan from a printed document) it is fairly thorough.
Rates each grade a little more difficult than the others. Very clear table layout.