Harry Potter, James Patterson and Oprah Winfrey’s book club aside, Americans — particularly young Americans — appear to be reading less for fun, and as that happens, their reading test scores are declining. At the same time, performance in other academic disciplines like math and science is dipping for students whose access to books is limited, and employers are rating workers deficient in basic writing skills.

That is the message of a new report being released today by the National Endowment for the Arts, based on an analysis of data from about two dozen studies from the federal Education and Labor Departments and the Census Bureau as well as other academic, foundation and business surveys. After its 2004 report, “Reading at Risk,” which found that fewer than half of Americans over 18 read novels, short stories, plays or poetry, the endowment sought to collect more comprehensive data to build a picture of the role of all reading, including nonfiction.

In his preface to the new 99-page report Dana Gioia, chairman of the endowment, described the data as “simple, consistent and alarming.”

Among the findings is that although reading scores among elementary school students have been improving, scores are flat among middle school students and slightly declining among high school seniors. These trends are concurrent with a falloff in daily pleasure reading among young people as they progress from elementary to high school, a drop that appears to continue once they enter college. The data also showed that students who read for fun nearly every day performed better on reading tests than those who reported reading never or hardly at all.