I have to wonder why an instructor would worry about a little thing like a comma being used incorrectly when it seems to me that a comma before "and" has always been accepted both ways. LOL I was taught to put a comma whenever you would naturally pause in a sentence and I have always followed that rule and never been corrected on a comma - either for leaving one out or putting one in anywhere in an essay.
It is only in the past few years that I have started using hyphens, and I use them all the time now. I love them. My grammar book from about 40 years ago says that they can be used in place of brackets but I didn't used to know that. Since my writing now is not for academia, I am going to continue using hyphens whenever I want.
I do think that there should be a recommended grammar reference for a school that a student and teachers can consult so that they are all on the same page.
