ST. PAUL, Minn. (AP) -

Minnesota parents have been warned that their children may receive lower test scores now that the state has adopted new national benchmarks known as the Common Core State Standards.

Education Commissioner Brenda Cassellius alerted parents in a letter last week. Minnesota Public Radio reports she wrote that because Minnesota is using more rigorous standards to teach English arts, schools also gave students more challenging tests to measure their progress toward meeting the higher expectations.

She says that means reading scores might look like they've dropped when they come out this summer. But she says it's not appropriate to compare the new scores with a previous year's because they measure different sets of expectations.

Minnesota has adopted the Common Core standards only in reading. The state has more rigorous math standards.