If your school district is fortunate enough to have an Art program budget it is because they are operating under specific academic standards that aim to accomplish a goal for the district.
These standards do follow the same academic goals of any other school subject such as Math, Science and Language Arts. Moreover, you will find that several of the 21st century teaching Art standards are connected to Math and Language Arts. Therefore, when you are graded in Art class, the teacher is not really putting a grade on your product, but on the standards and skills that the projects aim to have you perform.
For example, typical Art standards in the elementary school (for VA-Visual Arts) include:
VA3: Subject Matter, Symbols, and Ideas: The student chooses and evaluates a range of subject matter, symbols, and ideas.
VA4: History and Culture: The student demonstrates understanding of the visual arts in relation to history and culture.
VA5: Characteristics and Merits of Work: The student reflects upon and assesses the characteristics and merits of his/her work and the work of others.
As you can see the teacher is evaluating the student in three different aspects of Art interpretation. None of the standards make mention on whether the student can paint, draw, or color. It is a much more in-depth correlation that aims to be created between art skills, life skills, and analytical skills under a cognitive perspective. This is why the National Endowment for the Arts (NEA) is so involved in the maintenance of Arts and Humanities program in the American school system.