The Education Commission of the States says 32 states have passed legislation designed to improve third-grade literacy. Retention is part of the policies in 14 states, with some offering more leeway than others.
Backers say retention policies put pressure on teachers and parents to make sure children succeed.
But opponents say students fare better if they're promoted and offered extra help. They say holding students back doesn't address the underlying problems that caused them to struggle and increases their chances of dropping out of school.