The National Center for Education Statistics compared data from the National Assessment of Educational Progress, given to samples of students across the country, and the tests required by the No Child Left Behind Act.
"Today's study confirms what we've known for a long time: States are setting the bar too low," Duncan said. "In all but a few cases, states aren't expecting students to meet NAEP's standard of proficiency. Far too many states are telling students that they are proficient when they actually are performing below NAEP's basic level."
No Child Left Behind allows states to set their own standards with their own tests.
The NCES researchers found most of the difference between states on the percentage of students who show proficiency on the tests stems from how rigorous the standards are, with fewer students demonstrating proficiency in states with high standards.
The NAEP assessments are given to students in the fourth, eighth and 12th grades.
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