The standards are being implemented in 45 states and the District of Columbia, but critics say they were written in private and never tested in real classrooms, and that educators aren't familiar enough with the standards to use them. The standards also come with a multi-billion dollar price tag.
"Children are coming home with worksheets and their parents don't recognize it," said Emmett McGroarty, a director at the American Principles Project, a conservative group that opposes the standards. "Common Core is reckless in what it's doing to children."
Common Core's supporters think the worries are overblown and miss nuances of the sweeping changes that spell out the reading and math skills that students should have at each grade level, from kindergarten through high school.
But even the most vocal supporters admit they cannot guarantee the standards will succeed.
There's one thing both sides agree on: When fully implemented, Common Core stands to reshape the vast majority of American classrooms.
Critics — parents, teachers and tea partiers alike — argue that states were pressured to sign onto the Common Core standards to get federal economic stimulus money to keep teachers on the job.
In fact, to qualify for more than $4 billion in aid, states had to put into place standards to prepare students for life after high school and test student performance. Common Core wasn't specifically prescribed, but the Obama administration clearly signalled it was the preferred option starting in 2009.
"Normally, to go through standards it would take years," said Bill Evers, a researcher at Stanford University's Hoover Institution. "In California, we had six weeks."
Such quick approval resulted in new standards that some didn't fully understand.
For instance, the standards include tougher approaches to math — such as rigid motion in geometry — over more common approaches. "It has never successfully been used in K-12 education in the United States, in any state, in any country," Evers said of rigid motion.
At the same time, Common Core puts a greater emphasis on critical thinking needed as adults. There is a greater emphasis on non-fiction and technical selections, more likely needed in the workplace than sonnets.
To critics, it smacks of a federal reading list.
Teachers can still pick their own passages but Common Core provides examples as suggestions. If teachers have better ideas, they're free to use them. Literature and history aren't abandoned. For example, the recommended reading has a Pablo Neruda poem listed on the same page as the Constitution's Bill of Rights and a Ralph Waldo Emerson essay.
"There is no prescription as to how these should be taught. There's no one pedagogical standard how these should be taught," said William Schmidt, who heads the Center for the Study of Curriculum at Michigan State University.
Adds Robert Rothman, a senior fellow at Alliance for Excellent Education: "There's no such thing as a reading list."
But critics aren't buying it.
"Everyone claims there's all this local control and the ability for teachers to do what's best for teachers," said state Rep. Tom McMillin, a Michigan Republican who has led the push to eliminate the standards. "But as long as you have the assessment tied to the Common Core, you are teaching to the tests."
Those tests have been a sticking point for Common Core's critics, especially liberals and parents who worry the tests are too stressful for their children. Other critics worry the tests are giving government too much information about individual students.
Testing has been part of schools for years. As part of the Bush-era No Child Left Behind education law, testing was mandated so states could identify schools that were working and those that needed improvement.
But many critics point to the financial cost.
The conservative Boston-based Pioneer Institute estimates the total cost of Common Core will be almost $16 billion over seven years. The new tests alone would cost $1.2 billion during that same period, the think-tank says.
That has inspired concern among parents.
Hundreds gathered at the University of Notre Dame for a conservative conference about the standards. Activists are trying to stop the standards or roll them back at statehouses. And one Maryland man was arrested after he interrupted a town hall-style meeting by telling parents, "Don't sit there like cattle."
"Parents, you need to question these people. You need to do your research," Robert Small shouted as he was being led from a session meant to explain the new standards. "Is this America?"
According to an Associated Press-NORC Center for Public Affairs Research poll of parents this fall, 52 per cent of parents said they'd heard "only a little" or "nothing at all" about the standards. About a third of parents were unsure whether their state was adopting them.
That has left open the door for critics to fill in the blanks.
"Think of it as Obamacare for schools," the conservative American Principals Project says in a video on its website. "Did you know that they're replacing our American education philosophy of citizenship, individuality and unlimited potential with a European approach that sees us all as cogs in a state machine?"
That leaves some education leaders smarting.
"This is political," said Florida Gov. Jeb Bush, a Republican weighing a White House bid in 2016. "Meanwhile, back at the ranch, we have huge swaths of the next generation of Americans that can't calculate math, they can't read, their expectations in their own lives are way too low."
Education Secretary Arne Duncan, too, has little patience for the criticism. After Rep. Matt Salmon, R-Ariz., called Common Core a "federal takeover of the curriculum," Duncan scolded him.
"It's not a black helicopter ploy," Duncan said.
And in Richmond, Duncan sarcastically said parents are just now realizing that their schools aren't as good as they imagined.
"It's fascinating to me that some of the pushback is coming from, sort of, white suburban moms who — all of a sudden — their child isn't as brilliant as they thought they were and their school isn't quite as good as they thought they were, and that's pretty scary," Duncan said.
He said later he regretted the remark.
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EDITOR'S NOTE _ This is the second in a package of three stories exploring how teachers are incorporating Common Core State Standards, academic benchmarks adopted by 45 states and the District of Columbia, in the classroom, why those standards are being criticized and how they've created strange political bedfellows.