American high-school seniors’ performance in math declined from 2013 to 2015, while students’ reading achievement has shown no improvement, according to a federal report released Wednesday. The National Assessment of Educational Progress results also found a decrease in the percentage of students in private and public schools who are prepared for college-level work in math and reading. The test, which was given in 2015, showed 37 percent of students were considered prepared for college coursework in math and reading. In 2013, the last time the test was administered, 39 percent of students were thought to be ready in math while 38 percent were prepared in reading. Though 82 percent of high-school seniors graduated on time in 2014, the NAEP results indicate that many seniors would have to take remedial courses if they decide to attend college.