Young boys across the country have trailed their female classmates in language arts proficiency for at least four decades, but over the last four years, the gender gap in New Jersey's public schools has widened, test results released last week show.

Between 2009 and 2012, the percentage of fourth-grade girls who passed the reading section of the annual NJ ASK test held at about 65 percent, while the share of boys who passed declined by 8.1 percentage points.

This year, nearly half of the state's fourth-grade boys failed the test.

Male students' declining reading proficiency is evident to some degree in every grade and in every demographic subgroup, according to superintendents, who said they don't understand why this is happening or how to solve the problem.

Even as the language arts gap has grown, the disparity in math scores has almost disappeared. For decades, male students outscored their female counterparts, but girls have now caught up.

"The stereotypes don't hold true anymore," said North Brunswick Superintendent Brian Zychowski. "Our girls are scoring just as high as boys in math, but the boys are struggling with reading. I don't know why. I can't explain it."

Though state Department of Education officials are aware of the gap between male and female student proficiency in reading, they have no plans to address male student achievement specifically, said Barbara Morgan, a department spokeswoman.

"We want all of our students to retain proficient scores in math and language arts at all grade levels," Morgan said.

Aaron Pallas, a professor of sociology and education at Columbia University's Teachers College, said the shift in fourth-grade males' reading performance in recent years may not be cause for concern, but certainly indicates a need for further analysis.