Unions and their allies are trying to flex their muscle in state legislatures, pushing for labor history to be included in social studies curriculum and hoping a new generation of high school students will one day be well-educated union members.

But the results are instead shaping up as a reminder of the tough political landscape faced by organized labor. In six states, opponents have pushed back against demands that teachers offer lessons about the first craft unions in the 19th century, the large-scale organizing drives that powered the growth of industrial unions in the 1930s, the rise of organized labor as a political machine and other highlights of America's union movement.

California and Delaware are the only states with laws that encourage schools to teach labor history.

Kevin Dayton, a policy consultant to non-union construction companies in California, said the legislation was pushed by unions to boost their ranks.

"They believe that one of the reasons young people are not organizing in unions is because they're not taught in schools the benefits of being in a collective workforce," he said.

Ed Leavy, secretary-treasurer of teachers union AFT Connecticut, said the opposite is the case: "It's not that labor unions are demanding this so we can increase the ranks. It's people preventing this so we don't."

The legislation proposed in Connecticut was benign, Leavy said. It would have helped teachers with resources such as textbooks and instruction guides.

Steve Kass, a member of the executive board of the Greater New Haven Labor History Association and a backer of the legislation, said Connecticut's legislation could have bolstered the union cause.

"We're losing a generation of workers who don't have an understanding about the union movement," he said.

The measure failed this year for a third consecutive time even after supporters agreed to a compromise to include lessons in the history of capitalism. Opponents had many arguments against the measure.

Joshua Katz, a math teacher at the Oxford Academy in Westbrook, told lawmakers that decisions about curriculum belong to teachers and students, not the legislature.

"In general, I'm opposed to all of this top-down legislation," he said.

The state's largest business group, the Connecticut Business and Industry Association, said the legislation would have diverted resources from teaching core curriculum and closing the state's achievement gap.

And although backers say the legislation would not have required schools to teach labor history, Robert Labanara, state relations manager at the Connecticut Conference of Municipalities, said the state Board of Education would have been ordered to help and to encourage school boards to include the history of labor and capitalism in curriculum. That's less benign than it appears, he said.

"It's not uncommon in Connecticut to see this inch-by-inch law," he said. "It's one thing one year and becomes more of a financial and administrative burden down the road."

Various versions of labor history legislation have failed over the years in Illinois, Massachusetts, Pennsylvania and Tennessee, according to the National Conference of State Legislatures. Legislation also failed calling for labor history and collective bargaining to be taught in Vermont.

The Connecticut Legislature has already enacted measures requiring the state Board of Education to help and encourage local schools to provide curriculum materials for lessons about the Irish famine, African-American history and Holocaust studies.

Steve Armstrong, president of the National Council for the Social Studies and a West Hartford teacher, says squeezing another course into an already crowded school year could be difficult.

"It would be great if we can teach six weeks on the Irish potato famine, but it ain't going to happen," he said.

To Leavy, labor history could introduce students to early labor leaders such as Eugene V. Debs in addition to industrialists who are familiar to most Americans.

"You hear Rockefeller, you hear Vanderbilt," he said. "You don't hear Debs. The world is bigger than this."