Kristina Brant makes bio-diesel from algae in Chemical Analysis research class at Thomas Jefferson High School. (Charlie Archambault for USN&WR)

American teens are adept at conducting scientific experiments, but only if they don't stray beyond the basics, according to assessment results released Tuesday by the National Center for Education Statistics.

Seventy-five percent of high school seniors successfully completed straightforward experiments as part of the 2009 National Assessment of Educational Progress (NAEP) science exam. When tasked with more complicated experiments, only 25 percent came to the correct conclusion.

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Students have even more trouble explaining their results and drawing conclusions from the data they collected during the experiments. Only 11 percent of the 12th-grade students were able to do so, according to "The Nation's Report Card: Science in Action," which detailed results for students in grades 4, 8, and 12.

In a competitive, technology-dominated society, simply following instructions will not cut it, Alan Friedman, a member of the National Assessment Governing Board, the policy arm of the NAEP, said at a panel discussion of the results on Tuesday.

"Testing to see how much students can memorize and how well they can follow the instructions is no longer good enough," Friedman said. "It's crucial to know if students understand … how to draw the best of all possible solutions."

[Find out why STEM education is vital to the U.S. economy.]

Approximately 2,000 students at each grade level were selected to conduct either hands-on or interactive computer-based experiments as part of the annual NAEP science assessment. Experiments for students in grade 12 included testing and analyzing water quality, investigating the heat capacities of different metals, and classifying stars.

The new tasks allow stakeholders to get a more complete picture of students' problem-solving abilities than traditional paper-and-pencil exams, David Driscoll, chairman of the National Assessment Governing Board, said in a statement Tuesday.

Improving students' abilities to perform in-depth scientific analysis requires more than testing, Jack Buckley, commissioner of the National Center for Education Statistics, said at Tuesday's panel.

"It's not enough just to have a day at the end of the year when you walk in and drop these tests on kids," Buckley said. "It has to be part of the curriculum."