For each semester of co-op you can sign up for 1 or 2 credits of co-op class (UN 3002). If you need to be a full-time student during your co-op then you need to be signed up for 2 credits.
Yes, your co-op class is graded. Your employer will do a midterm and final evaluation on your work, and this evaluation will be submitted to Michigan Tech. You will be asked to do a midterm and a final evaluation of your employer as well. Lastly, to complete your co-op you must write a final report. All of this is used to determine your grade for the class.