I use what you defined as growth standards. My classes are mixed grades, some who have had several years of art, many who have had no art ever. (We don't have elementary art) I also have lots and lots of IEP's, in some hours it is the rule rather than the exception. So comparing with other students or some ultimate standards would be meaningless.
To be completely honest, probably what I end up grading on primarily is attitude. If they listen, try, make an effort and are generally engaged with the project, they will do fine. I know it is quite possible to be a good artist and never be a gifted draftsman, so attitude is what makes the difference.