The competition kicked off on Tuesday with computer-based tests and reaches its climax on Thursday with nationally televised finals producing a winner who goes home with $30,000 in cash and other prizes.
More than 11 million children have taken part in qualifying spelling bees over the past school year, with the best of the best advancing stage after stage toward the nationals.
Seven weeks ago, organizers caused a stir when they declared that for the first time in more than eight decades of competition, this year's contestants would have to prove their ability to not just spell obscure words, but also define them.
The reaction has been "very enthusiastic", said National Spelling Bee Executive Director Paige Kimble, the 1981 champion.
"I've had many parents and spellers approach me this week, thanking me (because) they realize that this raises the prestige of the achievement of making it to the Scripps National Spelling Bee."
Learning to be a perfect lady proves fruitful