From a kid's point of view, they're perfect: brightly colored, fast-moving, noisy and annoying to adults.

From a teacher's point of view, they're little plastic orbs from hell, and a number of local principals have banned them from their elementary schools.

Newton's Yo-Yo. Glowing Clackers. Klicka. By any name the toy is basically the same -- a plastic arm from which hang two plastic balls, each suspended from two plastic cords. With a flick of the wrist, the balls slam together with a sharp CLACK and then spin around to slam together again and again and again. It is the sort of sound that has driven parents mad. It is the sort of sound that makes childhood worthwhile.

In the past six months, the Smithsonian Institution's Air and Space and American History museum shops have sold 12,000 of the original Newton's Yo-Yos at $4.50. Fascination Toys and Gifts, the Seattle company that makes the Newton's Yo-Yo, has moved more than 850,000 in four years. In New York they have been clacking away for months, and now every Washington street vendor seems to offer $2 versions, hot pink, green and yellow knockoffs of the gadget.

"Oh, yes!" moaned Carolyn Preston, principal of Bunker Hill Elementary at 14th Street and Michigan Avenue NE. She knows the toy. She hates the toy.

"Anything that says, 'Noise!' -- they go to it," Preston said of her students. But when the clackers first appeared in her halls on Monday she said, "Let this be the last day."

Supposedly, Newton's Yo-Yo is an Educational Toy, magically imbuing its user with an understanding of two of Newton's laws of motion. (You remember -- A body in motion tends to remain in motion, and for every action there is an equal and opposite reaction.) But to the kids who use them, the attraction is far from educational.

"They make noise," explained 8-year-old Washington resident and clacker expert Dabney Shannon. Dabney attends Meyer Elementary at 11th and Clifton streets NW, a clacker-free school. "You bring them in, they're going to take them and throw them in the trash," he said outside the school as he demonstrated the proper technique with a toy provided by a reporter.

"They make too much racket in the hallway," said 9-year-old Jessica Easterling. "But we go to lunch and the kids sneak them under their shirts."

"Then the teachers take them," said Dabney.

"And the kids get an attitude," said Jessica.

The school day was over, and while Dabney and Jessica discussed the merits of clacking, the familiar sound began to ricochet down the street as the clandestine objects were released from their daylong hiding places. One younger boy, certainly no older than 3, stood nonchalantly flicking away.

Dabney offered that they were everywhere. "They even," he said, "have them in Texas."

They do not, however, have them at East Silver Spring Elementary School, at least not yet. "We only go up to third grade," said Principal David Rotter. "Our kids still want to please."

Just like the urge not to please adults, the clacker is far from new, but rather a perennially returning toy that Preston remembers from the early '70s. "I've seen it before," she said with the weariness only a teacher can muster. "What goes around comes around."

But years ago parents masked their hatred of the noise with the warning that the clacker balls, like most objects in the world, could put your eye out. In one school outside Philadelphia, letters were sent home to parents warning against the balls, claiming they had been known to shatter.

And in fact the Consumer Product Safety Commission did investigate clacker balls and in 1973 issued a set of regulations on the toy. "Sometimes they would come off the strings and go flying through the air," said safety commission mechanical engineer John Preston, proving those mothers right.

Apparently toy technologists have spent the intervening years mastering the technology. Unlike today's clackers, the classic balls were made of heavy lucite or metal and hung from strings. (A limited Washington Post test of the new toys, measured against nostalgically remembered late '60s clackers, suggests the old toy was more challenging. The thrill of danger is gone.)

The safety commission is actually now considering changing the regulations after an appeal by one toy importer whose clacker balls failed one element of the clacker test. "There's a test in which a five-pound weight is dropped from a specified height onto each of the balls," said John Preston. This particular set broke under the weight, but "that test is equivalent to something like 1,000 times the energy they see in normal use." Yes, Preston agreed, it's a pretty stringent test, and he thinks the regulations may be modified.

But the real problem -- the NOISE -- is not something the commission needs to worry about.

"Fortunately," said Preston, "our regulation doesn't address that."

And Ernie Pazmany, senior buyer for toys for the Smithsonian shops, offered this bit of wisdom. "Hey, you get a choice. You want that or Nintendo? If it was a choice between Nintendo and Newton's Yo-Yo, I would go with Newton's Yo-Yo."

Clack clack clack clack clack.