Seems like it's already part of the California standard for 1st grade: https://www.ixl.com/standards/california/math/grade-1 https://www.ixl.com/standards/cali

Seems like it's already part of the California standard for 1st grade: https://www.ixl.com/standards/california/math/grade-1 https://www.ixl.com/standards/california/math/grade-1 E.g. "Find the missing number: _ + 1 = 5". Same thing with subtraction. Based upon my experience with my 6 year old (in a public California elementary school), they actually seem to teach math in a huge variety of ways in 1st grade. Word problems, number problems, relationships between plus and minus, and boatloads of ways to solve any given problem. I think they introduced it in Kindergarten too. But it was way beyond her at the time.