The academic performance of 15-year-olds in the United States has stayed relatively the same in recent years, but with other nations improving, American students are slipping behind their international counterparts, according to a study released Tuesday.

The National Center for Education Statistics (NCES) released data on the 2012 academic performance of 15-year-olds around the world in three subjects: reading, mathematics, and science.

“We are not seeing any improvement in the U.S. … our ranking is slipping because other countries are improving,” said Jack Buckley, NCES commissioner.