I think I would have to go back to Cub Scouts for my first exposure here. No doubt this was discussed as current [hole] flow. At any point after that, my best recollection is that I was aware of both concepts. One of my science fair projects was a Van de Graaff generator, which clearly conveys the concept of electron flow. That was in the ninth grade, but I worked from dad's college physics books, so it's hard to be sure of what was taught in class.
Zooby, I think you needed at least a third option, so I didn't vote.