How do you assess student artwork?

When assessing student artwork, I take many approaches in evaluating student's learning.
I will use summative assessment, such as a portfolio to take a look at how a student has grown and progressed during their time in my classroom.  I might also use an authentic assessment, which  is a great tool to use in art.  This is useful when a student his handing in a final project.  Using a rubric can outline key learning objective and include a student's reflection of what they learned.  If a student can provide in writing what they have learned, I will know that they are learning what I am teaching.  Students should know what I am grading before they start a project and if they meet the criteria they will learn.  Some students need more structure and guidelines, while others may need more freedom.  This is up to my discretion based on a student's individual needs.