S:  How many is three 7s, Mommy?
A: Think about it.  Tell me what you decide.
S:  Well...7 is 3 and 4.  So two 4s is eight, and two 3s is six.  That's 14.  With one more 4, that's 18.  And one more three is...21.
Is this really how I did math before I memorized the multiplication tables?!  Surely not.  Our boy has an orderly mind.  It's fun to hear it in action.