* 29,000 teachers, support staff involved in walkout
* Parents of 350,000 students scrambling for childcare
* Negotiations again fail to reach agreement
Thousands of public school teachers marched in downtown Chicago on Monday as the first strike in a quarter century showed no signs of ending soon in a dispute over reforms sought by Mayor Rahm Emanuel and endorsed by President Barack Obama's administration.
Some 29,000 teachers and support staff in the nation's third-largest school system were involved, leaving parents of 350,000 students between kindergarten and high school age to find alternative supervision.
"There's no excuse for either side for not coming to an agreement," said Faith Griggs-York, mother of a first-grader at Agassiz Elementary School, as she dropped her daughter off at a community center a mile from the school.
"I think both sides, because of what they are doing to parents and because of what they are doing to kids, should be embarrassed," Griggs-York said.
The teachers' union called the strike Sunday night after months of negotiations did not resolve major disagreements over how teachers will be evaluated and giving school principals more authority over hiring.
The union and school district negotiated throughout Monday, but when School Board President David Vitale emerged from the talks, he said no agreement had been reached.
"We have said to them (the union) again that we believe we should resolve this tomorrow, that we are close enough to get this resolved," Vitale said. The teachers union did not immediately respond to a request for reaction to Vitale's comments.
A large crowd of striking teachers in red T-shirts rallied in downtown Chicago on Monday afternoon. Police officials at the scene estimated the crowd at around 10,000.
The rally had a carnival atmosphere but among the signs calling for a fair contract were plenty of homemade ones aimed at Emanuel, a Democrat, including "Fight Rahmunism" and "Actions Speak Louder Than Rahm."
"This is not about money. It's about working conditions and class sizes that haven't changed in 35 years," said Karen Kreinik, 46, a pre-school teacher at De Diego Academy. "It's absolutely shocking to me that we have a Democratic mayor who's anti-union."
Emanuel is among a number of big city U.S. mayors who have championed school reforms and Obama's education secretary, Arne Duncan - a former head of Chicago public schools - has endorsed them.
The school district's charter schools, which account for about 12 percent of students, opened as usual. The mayor wants to expand the number of charter schools, which are publicly funded but non-union.
Churches, community centers, some schools and other public facilities opened to care for thousands of children under a $25 million strike contingency plan financed by the school district. The children were supervised half a day and received breakfast and lunch, allowing some parents to work.
The union has called the plan to care for children during the strike a "train wreck." It warned that caregivers for the children do not have proper training, and there are fears of an increase in gang-related violence in some high-crime areas.
About 20 teachers picketed in front of Overton Elementary School on Chicago's South Side, wearing red T-shirts, carrying strike signs and singing "We're not gonna take it," the chorus from the rock band Twisted Sister's popular anthem.
Several passing cars honked in support, prompting loud cheers from the striking teachers.
Chicago's South Side, often mentioned by first lady Michele Obama in reference to her humble roots, is one of the city's poorest districts and has a large African-American population.
The Chicago confrontation also threatens to sour relations between Obama's Democratic Party and labor unions before the presidential election on Nov. 6.
While Obama is expected to win the vote in Chicago and his home state of Illinois, union anger could spill into neighboring Midwestern states such as Wisconsin, Michigan and Ohio, where the race with Republican challenger Mitt Romney is much closer.
White House spokesman Jay Carney said Obama was aware of the situation in Chicago. "We hope both sides are able to come together to settle this quickly in the best interest of Chicago's students," Carney said.
Campaigning in the battleground state of Ohio, Romney criticized the teachers union. "I want our kids to have the skills they need for the jobs of tomorrow and that means put our kids first and put the teachers' unions behind."
Emanuel said again on Monday that teachers should be evaluated based on student performance on standardized tests.
Union President Karen Lewis, who has called Emanuel a bully, said standardized tests do not take into account inner city poverty as well as hunger and violence in the streets.
More than 80 percent of Chicago students qualify for free lunches because they come from low-income households, and Chicago students have performed poorly compared with national averages on most reading, math and science tests.
Union officials said more than a quarter of Chicago public school teachers could lose their jobs if they are evaluated based on the tests.
"Evaluate us on what we do, not the lives of our children we do not control," Lewis said on Sunday.
Dick Simpson, a former city council member, or alderman, said that past Chicago mayors would have called negotiators to the mayor's office to get a deal by offering the union concessions. But dire financial straits preclude Emanuel from throwing money at the problem. The last Chicago teachers strike in 1987 lasted 19 days.
"Most parents now are supporting the teachers. If the strike were to go on that long, the public would be mad," said Simpson, a political science professor at the University of Illinois at Chicago.