New test results place American high schoolers well below their global contemporaries in mathematical literacy. The Program for International Assessment 2015 scores, released Tuesday, confirm a downward trend that appears to track the rocky implementation of the Common Core State Standards.

PISA tests how well fifteen-year-olds stack up against their global contemporaries. In math American teens rank 20 points lower than the international average—and 12 points lower than their own 2012 average. A yearly exam, the PISA rotates between reading, science and math so that a comparative ranking of the world’s teens rolls out once every three years in each subject.