"Six, plus one, plus two, minus four, plus one, plus two, minus six, plus five, plus two, minus four, plus two." As Sakabayashi recites the numbers, the two children rapidly push the abacus beads up and down, using only their thumbs and forefingers. "The answer is seven," says Nathan. "Right," says Sakabayashi.

The King children take weekly abacus lessons at the Japanese Abacus Math School (JAMS), in Sakabayashi's house in Tigard. Sakabayashi conducts classes in both English and Japanese. A manual calculator introduced to Japan from China in the 1500s, the box-shaped abacus is made of beads that serve as counters, which users push back and forth along metal rods, clicking their way through addition and subtraction, long division and multiplication.

In many Asian countries, the abacus is still used to teach math to elementary school children. Advocates argue that the use of the abacus is one of the main reasons children in these countries consistently rank at the top of international math comparisons.

"I'm very angry about the use of calculators in this country," said Sakabayashi, whose 4-year-old daughter, Aya, is already a whiz on the abacus. "With the calculator, kids just punch in the numbers. With the abacus, we have to use all our functions as human beings: eyes, fingers, ears."

Before starting JAMS, Sakabayashi taught abacus lessons at Richmond and Woodstock Elementary Schools. Nathan, a student at Richmond, has been taking abacus lessons since he was in first grade. His mother, Miriam King, is one of Sakabayashi's biggest supporters.

"I've been looking for an abacus teacher since I had kids," said King. "I was exposed to the abacus as a child, and it is the best way to teach kids how to do mental math."

At first, Nathan didn't like the classes much, acknowledged King. "But when he started to see himself excel, he loved it."

Using textbooks Sakabayashi has had sent from Japan, the two children work on addition and subtraction problems during class. Pushing beads back and forth, Nathan solves strings of two-figure math problems fast enough to make a reporter's head spin. In graceful, precise gestures, the children clear the beads with their forefingers after each problem is finished.

Most challenging of all is the "magic abacus," a fanciful term for mental calculation. As Sakabayashi recites a series of numbers, the kids must solve the problem by moving their fingers on imaginary beads. "The answer is one," says Nathan. "That's correct," says Sakabayashi. "Yes!" says Nathan triumphantly.

There is some competition between the two siblings in the abacus class, said King. "But competition is a good thing," she said. "And they learn to respect the fact that one is older and knows more and the other is younger and still learning."

Mastering the abacus, not to mention the "magic abacus," takes a lot of concentration and practice, said Sakabayashi. "But young children learn things quickly."

Details: 503-624 9766, www.JAMSportland.com.