Six-year-old Verdi's math flashcards are color-coded according to what memory trick he's supposed to use with that fact.   Today, during the part of math drill where he has to shuffle the cards, Verdi began to chatter excitedly.   "Mama, did Native Americans live at the same time as the Celts and Romans?"

"Yes, some Native Americans."

"Well I'm putting all of my red facts alone, and the green facts next to the blue ones.  The blue ones are the Celts.  They're fighting the Romans who are the green ones.  The ones are the Native Americans and they're on another continent."

"Who are the yellow?"

"Um . . . "

"The Vikings!" his older stepbrother interjected.