The study comes at an important time in the debate over testing in U.S. schools. In recent years, politicians and educators have debated how much testing is necessary.
Historically, local and state governments have been responsible for schooling. In the 1990s, educators and politicians demanded that the federal government step in. They asked that state and local governments agree to education standards. Some schools in some states and cities were not doing well.
In 2002, Congress passed the No Child Left Behind Act. The law's goal was to improve standards at primary and secondary schools. It required states to find the substandard schools by testing them.
But many students performed poorly even though they graduated from high school. Some were not prepared for college or for a career. Politicians debated about using national standards to measure education across the US.
They never reached an agreement.
In 2009, some U.S. states began the Common Core Standards Initiative. Common Core sets milestones students should reach for English, Language Arts and mathematics. States that have adopted Common Core will test to measure student's success in the same subject areas.
However, local and state governments can also give their own tests. And those tests differ, even if they cover the same subject. This partly explains why schools give so many tests in the U.S.