Over the last 20 years, fictional writing produced by young people has become less creative, more linear and less likely to contain magical elements, a new study reports.

On the flip side, the study also found that adolescent visual artworks have become more complex and sophisticated.

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The findings, published in Creativity Research Journal, add to growing evidence that creativity is declining among U.S. students who are schooled to score well on standardized tests instead of thinking outside the box.

"With respect to writing, it's hard not to focus on the way the educational system has changed over the last 20 years, particularly the advent of No Child Left Behind that has really emphasized teaching to the test," said Katie Davis, an expert on human development and education who studies how digital media affects young people at the University of Washington.

"Emphasis on the five-paragraph essay and linear structures has not left a lot of room for risk-taking," she added. "Encouraging any sort of creative expression is very hard to do in the current era of high-stakes testing."

Imagination and creativity are essential for fueling innovation and unorthodox problem-solving strategies in business, culture, even sports. But while scientists have spent more than 100 years refining tools for measuring intelligence, said Jonathan Plucker, an educational psychologist at the University of Connecticut, Storrs, an intense focus on understanding creativity began in earnest just 15 or 20 years ago.

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One reason for the neglect is that creativity is harder to study. It can’t be assessed with multiple-choice questionnaires and instead requires time-consuming (and therefore expensive) reviews of people’s ability to solve problems.

The currently accepted gold standard for creativity assessment is the Torrance Test of Creative Thinking, which asks test-takers to do things like come up with unusual uses for ballpoint pens and other common objects. Since 1990, a study published in 2010 found, scores on the test have been steadily declining in the United States. That news led to headlines and concerns about the nation's "creativity crisis."

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Concerned that the Torrance test might not translate to real-life situations, Davis and colleagues collected examples of adolescent writing and visual art produced over a 20-year span, beginning in 1990. In the interim, the Internet became widespread and the focus of the U.S. educational system shifted. The researchers wondered how those trends might influence the creative output of young people.

To begin, the team collected more than 350 pieces of art published in a magazine called Teen Ink, which has showcased teen art, photography and writing since 1989. Half of the pieces ran in the early '90s. The other half ran more recently. Two trained visual artists rated each piece of art using a series of codes that assessed composition, background, stylistic approach and other details.

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Compared to artwork produced two decades ago, the researchers reported, recent teen works were more likely to fill the whole canvas and include more stylized cropping. Figures tended to be placed off-center, and works more often incorporated collage, found objects and digital manipulation. All of those details suggested a rise in creativity, Davis said, likely as a result of exposure through the Internet to a more diverse array of art that could inspire students. Today, there are also many more options for using computers to produce art.

Creative writing showed the opposite trend. When the researchers coded and compared 25 recent stories with 25 older ones that were published in an annual literary magazine by a creative arts school in New Orleans, they found that the older stories were more experimental.

One story from the early '90s, for example, included a character who visited a psychologist, and the psychiatrist was a crab. At the end of the story, the protagonist grabbed the crab with a pair of tongs and threw it in his suitcase, saying, "Tonight I dine on boiled crab!"

More recent stories tended to be grounded in reality with scenes of uneventful Thanksgiving dinners and accidental shootings. Recent stories were also more likely to progress chronologically instead of jumping around in time.

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Teachers are not to blame for the pressure to prioritize standards over creative thinking, Plucker said. Instead, it’s a system-wide issue that will need to shift towards giving students freedom to explore ideas before we’ll see a rebound in creativity.

Whether creativity is genetically determined or learned, he added, evidence suggests that just about all of us are underusing our imagination skills.

"Take any state accountability system, take No Child Left Behind, and show me any creativity or problem-solving indicators," Plucker said. 'They're not there. That tells you all you need to know."