WASHINGTON - A growing number of states are drawing a hard line in elementary school, requiring children to pass a reading test in third grade or be held back from fourth grade.

Thirteen states last year adopted laws that require schools to identify, intervene and, in many cases, retain students who fail a reading proficiency test by the end of third grade. Lawmakers in several other states and the District of Columbia are debating similar measures. Arizona passed a similar law in 2010 to take effect next school year.

Not every state requires retention; some allow schools to promote struggling readers to fourth grade as long as they are given intensive help.

Advocates of the new tough-love policies say social promotion - advancing students based on age and not academic achievement - results in high schoolers who can barely read, let alone land a job or attend college. Literacy problems are best addressed at an early age, they say.

Critics say the policies reflect an accountability movement that has gone haywire, creating high-stakes tests for 8-year-olds. The child, not the school, bears the brunt of the problem, they say, pointing to research that shows that the academic benefits of repeating a grade fade with time while the stigma can haunt children into adulthood.

"This is completely unsettling. I'm concerned about a number of those legislative initiatives," said Shane Jimerson, a University of California at Santa Barbara professor who has studied retention for 20 years and found that, from a child's perspective, being held back is as stressful as losing a parent.

"This is deleterious to hundreds of thousands of students," he said. "But children don't have a voice. If you were doing this to any group that had representation, it would not be happening."

Third grade has become a flash point in primary education because it's the stage when children are no longer learning to read but are reading to learn, educators say. If children haven't mastered reading by third grade, they will find it hard to handle increasingly complex lessons in science, social studies and even math.

In large, urban districts, retention policies can affect a large share of third-graders. In the District last year, for example, almost 60 percent of third-graders were not proficient in reading, according to the city's standardized tests.

"It's been that way for a long time," said D.C. Council member Vincent Orange, who is proposing a third-grade retention law that would apply to traditional and charter schools. "And we have to try something different. There has to be a full-fledged assault on the problem."

In some places, retention has morphed from an educational issue into a political fight.

Tony Bennett, Indiana schools superintendent, lost his elected position in November to Glenda Ritz, a teacher who ran because she was angered by Bennett's third-grade retention policy.

"It was the final straw," said Ritz, adding that her state should emphasize reading as early as kindergarten and help struggling readers well before third grade. She wants to stop retaining children based on standardized test scores.

Bennett, meanwhile, became state education commissioner in Florida, where the third-grade retention policy has served as a model for other states.

Ending social promotion has become so popular in some policy circles that Virginia Gov. Robert McDonnell, a Republican, boasted to a recent meeting of the National Governors Association that he had accomplished it, though Virginia's laws actually fall short.

"We essentially put an end to social promotion in third grade by major new third-grade reading incentives," McDonnell told a panel of other governors on Sunday. "I mean, we just do a disservice to these young people; we all see it in our schools. If they get passed along to eighth, ninth grade, it contributes to the drop-out rate if they're not able to read."

Literacy is a struggle for many U.S. children, with 33 percent of all fourth-graders reading below basic levels in 2011, according to U.S. data. Half of black and Hispanic fourth-graders were below basic in reading.