Elementary school teachers from 15 years ago are using some techniques the teachers used back in the early 70's.
Today in my Micro Principles classes, I discussed the basic difference between how accountants view firm profitability and how economists view firm profitability. In discussing how economists subtract out implicit and explicit costs while accountants subtract out only explicit costs in their formal work, I mistakenly wrote on the board that acct. profits < econ. profits. I explained it correctly, but wrote the inequality backwards.
An attentive student noticed my mistake and pointed it out, to which I replied, remembering when I first learned about inequalities in elementary school "Oh. I've got the alligator's mouth turned around." I said it lightheartedly with a smile, and and another one of my students laughed and said "that's how I learned it too." He's, probably 19 or 20. I'm 46. But we both learned inequalities the same way in our elementary schools.