Excel formula help

I have created a spreadsheet for my class that finds the MAX value in each row. This chooses the highest score that a student received on a standard or lesson after being able to take it multiple times. However, If a row is blank (student has not taken yet) then it automatically places a zero in the final column. How can I change that to where it leaves the final column blank until  the student completes the lesson and a grade is placed into the row. I am calculating the average of the final column (which right now is including all 0s).