Wow, this thread evolved quickly, I'm still back on the comma before and, and the comma before but part !!! I was taught back in the 50's and 60's, that before those two words it was rare to use the comma. It really depends on the sentence meaning going forward into the rest of the statement. And, ( as I just wrote) you would be downgraded for an essay exam by starting a new sentence with either word as well. Again, limited use. You will often see me writing with limited use of a comma before and, and but as well. I believe, the premise was to find a better way to vocalize your meaning, so as not to use those words as such, in either case.
I can recall thinking I was smart to write a certain way, just to be downgraded for the very thing I was being so smart about !
In school in the 80's ? I was in my 30's then and things had changed a whole lot. My kids were in school then and the school systems in the US had abolished a lot of things . Standards just continued down hill from there.