Mothers and fathers -- some with their kids in tow -- are marching with the teachers. Other parents are honking their encouragement from cars or planting yard signs that announce their support in English and Spanish.
Unions are still hallowed organizations in Chicago, and the teachers union holds a special place of honor in many households where children often grow up to join the same police, firefighter or trade unions as their parents and grandparents.
"I'm going to stay strong, behind the teachers," said the Rev. Michael Grant, who joined teachers on the picket line Tuesday. "My son says he's proud, `You are supporting my teacher."'
But one question looming over the contract talks is whether parents will continue to stand behind teachers if students are left idle for days or weeks.
Mary Bryan, the grandmother of two students at Shoop Academy on the city's far South Side, supports the teachers because she see "the frustration, the overwork they have." A protracted labor battle, she said, would "test the support" of many families.
Parents "should stick with them, but they might demand teachers go back to work," Bryan added.
To win friends, the union has engaged in something of a publicity campaign, telling parents repeatedly about problems with schools and the barriers that have made it more difficult to serve their kids. They cite classrooms that are stifling hot without air conditioning, important books that are unavailable and supplies as basic as toilet paper that are sometimes in short supply.
"They've been keeping me informed about that for months and months," Grant said.
It was a shrewd tactic, said Robert Bruno, professor of labor and employment relations at the University of Illinois at Chicago.
"This union figured out they couldn't assume the public would be on their side so they went out and actively engaged in getting parent support," Bruno said. "They worked like the devil to get it."
But, said some reform advocates, public opinion could swing against the union relatively soon if the dispute seems to carry on with no resolution in sight.
Juan Jose Gonzalez is the Chicago director for the education advocacy group Stand for Children, which has hundreds of parent volunteers and was instrumental in pushing legislative reforms in Illinois. He says parents "are all over the map" in terms of their support for teachers or the school district.
"Within a day or two, all parents are going to turn their ire toward the strike," Gonzalez said. "As parents see what the district offers and see the teachers not counter-propose, they will become increasingly frustrated with the grandstanding."
During the last Chicago teachers strike in 1987, Bill Werme and his wife got so angry they pulled their daughter out of public school and enrolled her in private school for second grade. Parents could face the same choice now.
"If it was me, my support would whittle away," Werme said.
Already, there are some parents who don't understand why teachers would not readily accept a contract offering a 16 percent raise over four years -- far more than most American employers are giving in the aftermath of the Great Recession.
Rodney Espiritu, a stay-at-home dad whose 4-year-old son just started preschool, said the low test scores he's read about suggest teachers don't have "much of a foot to stand on."
Chicago's history of labor strength is one reason why this dispute is seen as a test of organized labor at a time when unions' political influence is being threatened across the country.
"What you're seeing here is a massive show of solidarity that is as widespread as anything we've seen in decades," said Jorge Ramirez, president of the Chicago Federation of Labor.
On Tuesday, union President Karen Lewis said negotiations were still far apart, with the two sides having agreed to just six of 48 articles in the contract. She said it would be "lunacy" to expect an agreement before Wednesday.
In many ways, Chicago is the perfect place for teachers to wage this battle, Bruno said.
With an estimated half million workers in the metropolitan area belonging to a union and a full quarter of the workforce unionized -- a percentage rivaled only by New York and a handful of other big cities, Bruno said teachers have the most sympathetic public they could hope for.
"I do think if you were going to craft or design a strategy and determine the geographical space with the right politics, the right values, you couldn't do better than Chicago," he said.
Such an environment is the envy of other unions around the country that have been pushed around for years and forced into concessions they felt powerless to fight.
"I think many of our teachers are afraid of standing up because they fear retribution -- losing their jobs," said Keith Johnson, president of the Detroit Federation of Teachers, which walked out for 16 days six years ago. "There is a greater emphasis on going along to get along."
Unlike Chicago, where thousands of teachers could be seen marching in the streets, Johnson worried what might happen if Detroit teachers voted to strike again but failed to get full participation.
"The worse thing of all is to have an action and then have just 10 percent of your members take part," he said.
Chicago's union membership includes every teacher in the city except for those in charter schools.
Ellen Bernstein, president of the teachers union in Albuquerque, where only about half of the 7,500 teachers are in the union, said a strike in her district would fail.
"As long as only 50 percent of your teachers are in the union, it is clear we would not prevail. It takes solidarity -- and that's what Chicago has," she said.
At the same time, Chicago's stature as a union town raises the stakes for all unions. And it is particularly important to other teachers who are engaged in or are contemplating a similar tug-of-war with city officials.
"If you can weaken the capacity of the teachers union to represent its members in Chicago, then there is simply no place across the land where you couldn't do this," Bruno said. "It will mean that we'll be locked into a level of reduced union relevance for a generation."