Counting-By introduces multiplication. Counting-by or skip-counting is, we believe, the best way to help students build their multiplication facts, and though they will live in an age of ubiquitous spreadsheets and calculators, they still need to have mastered their multiplication facts to do any interesting math in their heads. Here they learn to build rules that count-by and in the process practice both counting-by and rule-making. Counting-by adds the same number again and again and their rule should do the same.