Washington, D.C. ? The math tests students take under the No Child Left Behind law are harder than the reading exams, a study finds.

States design tests for their students in both subjects in grades three through eight and once in high school.

By 2014, all students are supposed to reach the proficiency mark on those tests, which generally means they are working at their grade level.

What kids have to show they can do to be labeled proficient in math is typically harder in most states than what they have to do to in reading, according to a study released today by the Thomas B. Fordham Institute, a Washington-based education think tank.

The Fordham study also found many states are making it easy to score well on the tests given in elementary school but harder to pass the middle school tests.