“I’d just blurt it out,” he said in an interview while back home here this summer.

But Ruifan, 15, who goes by Derek in the United States, soon discovered that science was more than just facts and formulas meant to be regurgitated on tests.

At school in West Des Moines, Iowa, where he lived with a host family, his science teacher donned protective goggles and used a long-reach lighter to ignite a hydrogen balloon, just so students could get a firsthand look at the element’s explosive properties.

Then there was the day he and his classmates went up to the roof to learn about gravity by dropping basketballs, tennis balls and other objects over the edge. “Back in China I learned about gravity from a PowerPoint slide,” he said. “That’s it.”

The United States State Department does not break down its data on visas by age and school type, but anecdotal evidence here suggests that increasing numbers of middle-class families are looking for a way out of China’s test-taking gantlet.

“I didn’t want my son to become a book-cramming robot,” said Ruifan’s mother, Wang Pin, explaining why she sent him to live and learn halfway across the world. American educators and politicians have been warning for years that rising powers like China and India are poised to overtake the United States in science achievement. On a 2009standardized test that drew worldwide attention, students in Shanghai finished first in the sciences among peers from more than 70 countries, while the United States came in 23rd (right behind Hungary).

But even many Chinese educators are dismayed by the country’s obsession with stellar test results. Last fall they convened a conference on the topic in Shanghai.

“When American high school students are discussing the latest models of airplanes, satellites and submarines, China’s smartest students are buried in homework and examination papers,” said Ni Minjing a physics teacher who is the director of the Shanghai Education Commission’s basic education department, according to Shanghai Daily, an English-language newspaper. “Students also have few chances to do scientific experiments and exercise independent thinking.”

That message appears to be getting through to Chinese education officials, who are moving toward the American model of hands-on science learning. This summer, the Ministry of Education launched the latest in a series of campaigns aimed at shifting the focus away from standardized testing.

The ministry said the systemic fixation with testing “severely hampers student development as a whole person, stunts their healthy growth, and limits opportunities to cultivate social responsibilities, creative spirit, and practical abilities in students.”

But as with so many orders from the central government, it remains to be seen whether these guidelines, aimed at provincial education departments, will be adopted or ignored.

Meanwhile, preparation for China’s national university entrance exam continues to dominate the lives of secondary students. Known as the gaokao, or high test, the exam takes nine hours over two days, and some say it makes the SAT look like a pop quiz. Compounding the pressure, gaokao results are the sole factor used to determine university admissions.

This ironclad criterion, combined with the fact that most families have only one child, gives Chinese parents little incentive to encourage extracurricular activities, lest it divert their children from the slog of gaokao memorization. Critics say it also produces poorly socialized adolescents who are ill-prepared to face the challenges of the real world. Students have their own term for describing the way their teachers impart knowledge: “feeding the ducks.”

As a science teacher in the northwestern region of Ningxia, Wei Jinbao has seen firsthand how China’s education system transforms children into hardworking students with an impressive capacity for processing factual information. “Give them a problem and they will find the answer,” he said. “However, they can’t ask a good question.”

Like many Chinese science professionals, Mr. Wei is keenly aware that the country has yet to produce a Nobel Prize winner in the sciences whose research is homegrown. Over the years, he has tried to spark innovative thinking among his students, but he is missing a critical element: lab equipment, which most Chinese schools see as an unnecessary expense.

Asked why, he sighed in exasperation. “The entrance exam doesn’t test experiments,” he said.