Some school districts and teachers require students to learn the multiplication facts beyond the 9’s. It probably came about because many of the ten, eleven, and twelve facts are easy to learn (10’s add a 0, 11’s double the number). The 10’s have some merit conceptually, but you don’t really need a system to learn them. The 10’s, 11’s, and 12’s are actually the beginning stages of double-digit multiplication. Once a student has mastered the 0-9 times tables, double-digit multiplication is a snap.