I am not a teacher, but I asked my wife (who is continuing her education in graduate school for English) this question and she told that the 2nd comma in your list is called the oxford or serial comma. It is optional, so it is correct whether you use it or not. Check out this wikipedia link, it explains it pretty well.
Serial comma - Wikipedia, the free encyclopedia
According to the article, most American scholars suggest using the serial comma.
I hope this helps.