9 × 12 = 108 (1 + 0 + 8 = 9)
Notice that the two digits of each answer always add up to make 9,
and that each first digit of the answer is just one less than the
multiple. For example, 9×5=45, the answer will begin with one less than
the multiple 5, and the two digits of the answer must add to make 9,
therefore it can be nothing but 4 and 5, or 45. This is true in all
cases except 9×11 an already known answer, but also only 9's in this
answer. This simple idea, when once understood, will master the table
of 9's.
Be sure that the children realize that 7×4 in the tables of 7's are the
same in value as 4×7, so that the answer to 7×4 becomes familiar with
learning the table of 4's. Ask the question both ways 7×4 and 4×7.