This rules sticks with me. I always use a comma preceding an and when listing things.
I can remember in fifth grade we had a grammar worksheet and passed ours to another student for them to grade based on the teacher's and my friend whom was grading mine tried to mark me off for using the comma. Upon asking the teacher, though, she corrected him. I'm not sure why that memory sticks out, but it has enforced the comma preceding an and convention in me.
Perhaps it has had a negative impact on me though, as I tend to over use the comma when typing resulting in a large number of comma splices. I tend to place them in areas where I would pause in a sentence, which is not always appropriate grammatically.