New York is facing a growing rebellion against Common Core-aligned standardized tests. About 20 percent of the state's third- through eighth-graders refused to take the tests this spring, up from 5 percent a year earlier. As state education officials consider the possibility of sanctions against districts with large numbers of students opting out, they also promise a plan to boost participation.

Here are some details:

THE TESTS

The federal No Child Left Behind Act of 2001 requires states to test all students in grades 3-8 in English language arts and math each year. Students in New York are given the tests during two separate weeks in the spring, with each test being administered over three days in 60- to 90-minute sessions.

In 2013, New York aligned the standardized tests with new Common Core learning standards that most states have adopted to better prepare students for college and careers. The standards spell out what skills students in each grade should master and emphasize critical thinking, writing and real-world math.

The state's 2012 teacher evaluation law requires that student test scores be factored into the formula used to rate whether teachers are "ineffective," ''developing," ''effective" or "highly effective." Teachers with two consecutive "ineffective" ratings could be fired.

Student scores also are broken into four categories: well below proficient at the grade-level subject, partially proficient, proficient or excelling.

Test results are released over the summer.

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THE OPT-OUTS

The more than 200,000 of New York's 1.1 million third- through eighth-graders who refused to take the tests are part of a protest movement that is growing nationally.

New York is believed to have the largest rate of opt-outs so far, but resistance has been reported around the country, including in Colorado, Maine, New Mexico, Oregon, Pennsylvania and Washington. Robert Schaeffer of the National Center for Fair and Open Testing estimated a half-million students nationwide opted out of this year's tests, with numbers varying widely among states and cities.

The percentage of those opting out in New Jersey could rival New York's or reach into the teens, Schaeffer said. A spokeswoman for New Jersey's Education Department declined to release the figure Thursday.

Parents cite a range of concerns, including the amount of classroom time spent on test preparation at the expense of creative lessons and test-stress on their children. Others worry money is being diverted from classrooms to administer and score the tests and that results are released too late to do any good — after the school year has ended.

"For children in urban communities with increased class sizes and decreased funding, the tests are a way to prove that the schools are failing so they can be closed and re-opened as charter schools," said Morna McDermott, a founding organizer of United Opt Out, which issues state-by-state guidance on the topic.

In New York, numerous districts saw more than 30 percent of students opt out and some had more than 80 percent, data from the state Education Department showed. On Long Island, East Islip and Farmingdale saw more than 60 percent of students sit out. In western New York, West Seneca had 71 percent opt out.

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WHAT'S NEXT

Although federal money could be withheld if less than 95 percent of a district's students participate, that hasn't yet happened. Both U.S. Department of Education spokeswoman Dorie Nolt and state Education Commissioner MaryEllen Elia said their departments were in contact on the issue.

"We will be taking action in New York," Elia told reporters Wednesday, "and analyzing and figuring out what we need to do for districts to get more participation and also looking specifically, district by district and school by school, to figure out with the leaders of those districts exactly what happened there."

She said efforts would include getting parents to understand the importance of assessments in measuring progress toward the higher learning standards. On Thursday, she said a lack of communication with parents was partly to blame and also said the state should move toward administering the tests by computer so the results will be available sooner.

"The quicker that we get it back the more relevant it is," Elia said at a New York City forum on education sponsored by City and State.

Organizers of the opt-out movement appear undeterred. New York State Allies for Public Education is encouraging parents to hand in refusal letters for the 2016 tests on the first day of school.

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Associated Press Writer Karen Matthews in New York City contributed to this report.