Music and art instruction in American eighth-grade classrooms has remained flat over the last decade, according to a new survey by the Department of Education, and one official involved in the survey called student achievement in those subjects “mediocre.”

The survey, released on Monday, was conducted as part of a nationwide test of music and arts achievement administered last year. As the first federal effort since 1997 to examine instruction and measure student achievement in music and the arts, the survey has added new evidence to the debate about whether American schools are cutting back on the subjects they teach to concentrate on improving students’ basic skills.

In the test, formally known as the National Assessment of Educational Progress in Arts, administrators at 260 public and private schools were asked how much time they devoted to art and music instruction, and 7,900 eighth-grade students were tested on art and music concepts, a small sample compared with other federal assessments. For example, in 2007, the department tested 700,000 students in reading and math, and 29,000 in history.

The small number of students tested, and the 11-year gap since the most recent federal arts test, limited the assessment’s usefulness for reaching conclusions about achievement trends, federal testing officials said.