Second-graders Kayla and Brian used to play "Declare Math" without the 11- and 12-numbered cards. But that was before they began to better understand the numbers.

Now, on a hazy Monday morning, they sat facing each other on the floor playing the new card game. Each rhythmically threw down a card. They raced to shout what the two numbers added up to. The first and fastest correct answer awarded the winner both cards.

10 + 6? 16! Kayla wins.

6 + 5? 11! Brian, with a sly smile, was too fast.

9 + 8? 17! "Ahhh, man," lamented Kayla, 8, as Brian, 7, scooped up the cards again.

Engineer-turned-public-school-teacher Eugenia Duncan invented the game four years ago, frustrated that her high school students were more interested in playing cards than learning math.

Duncan grasped that the cards could be a key to her lessons. The game is deceptively simple. It combines a traditional deck and the game "Uno" into the card game Duncan calls "Declare Math."

Students play it such as they would "War" —- only the cards are numbered 0 to 12 and the first player to add, subtract or multiply the sum of two cards wins the hand.

"They prefer that [game] over anything else they do," said Kayla and Brian's teacher, Judi Martin, of DeKalb County's Rainbow Elementary School.

Martin introduced the game to her students in September and lets them play if they finish their lessons early.

"The kids enjoy doing it; then they end up participating more in their math facts," Martin said.

Duncan, a former DeKalb teacher, recently began to market the $4.99 game at declaremath.com.

Having so far sold 1,000 decks, she said the game worked because "these are not traditional flashcards. That's why kids get sucked into it."

Duncan's brainstorm demonstrates not only the necessity of classroom innovation but also the value of informal, alternative teaching tools that experts say belong in more classrooms.

University of Georgia education professor Michelle Commeyras points to research that suggests a connection between learning and what students may be accustomed to doing outside the classroom. Take video games: Commeyras has tutored a teenager whose third-grade reading level improved as the two played text-heavy games together.

"I don't think children are more motivated to learn for learning's sake," said Commeyras, adding that since not all educators feel comfortable using technology, a simple card game works just as well. "If [students are] doing something that's interesting to them, they do it; they just don't always realize they're learning."

Duncan agrees. "A lot of people are not comfortable with math because they're not comfortable with the basics," she said. "If you get kids more comfortable with the basics, it's like a cycle: The more comfortable you are, the more confidence you have."