My teacher showed me this when I was in 4th grade, in 7th grade math, I use these rules so often! It is helpful when dividing large numbers and learning mental math quickly. For higher level students, this is a great thing to make poster charts on. Ancher charts are great ways to remember things and it is very fun when you add color and pictures. This is in the 4th grade common core standards while also taking education to the next level.