Only about a third of American adults can name all three branches of government, and a third can't name any.

LOS ANGELES — Only about a third of American adults can name all three branches of government, and a third can't name any. Fewer than a third of eighth-graders could identify the historical purpose of the Declaration of Independence.

This slim knowledge of civics — and the potential risk it poses to American democracy — captured the attention of retired U.S. Supreme Court Justice Sandra Day O'Connor.

During a recent trip to Los Angeles, she talked up iCivics, an expanding online program aimed at middle school students.

The free curriculum includes lesson plans and games that are linked to subjects and skills that various states require students to master. The program also promotes public service projects.

O'Connor launched the effort that became iCivics in 2006, the year she retired from the court. It initially focused on the judicial branch alone, but "it became apparent pretty quickly it was needed across the board," she said.

"It's very disturbing," said O'Connor, 81, the first woman to serve on the nation's highest court. "I want to educate several generations of young people so we won't have the lack of public knowledge we have today."

Nationwide, her work has influenced a new civics education law in Florida and pending legislation in Kentucky and Tennessee.

Civics education involves explaining the structure of U.S. government, including the meaning and influence of the Constitution and its evolution over time. Advocates also emphasize the importance of getting students to engage in the democratic process, said Kathleen Hall Jamieson, director of the Philadelphia-based Annenberg Public Policy Center.

Limited knowledge about the three branches of government — executive, legislative and judicial — emerges starkly in Annenberg surveys, which also found that 15 percent of adults correctly named John Roberts as United States chief justice, but almost twice as many (27 percent) could identify Randy Jackson as a judge on the television show "American Idol."

Poor understanding of civics has persisted for decades despite increased college attendance, Jamieson said. "There is a base level of knowledge that is out there," enough to keep the country functioning, said Jamieson, "but it's a lot baser than some would like."

One problem may be a consequence of the federal No Child Left Behind Act, which emphasized reading and math instruction with required testing.

California students have suffered from that national trend, experts said, although they still are required to take three years of social studies in high school.