What are effective ways to assess what my students are learning?

How should I grade a student who has a disability? I have never been in favor of grading students with numbers. I think is horrible that this system is based on numbers to show how good a student is. But going along with the system this website has a really good point about how grades should be part of the student's progress. http://serge.ccsso.org/question_4_4.html