A nationwide assessment shows the vocabulary skills of Arizona students in fourth- and eighth-grade rank below the national average.

The findings released this week come from results of the 2009 and 2011 National Assessment of Educational Progress sponsored by the U.S. Department of Education.

The Arizona Republic reports that about a dozen other states and territories, including New Mexico, also ranked below the national average in the two grade levels. Poorer students demonstrated the largest gap in word knowledge.

The NAEP began testing students on their understanding of word meanings in 2009.

Arizona education officials say students' scores should improve once schools around the state implement new testing standards that emphasize working with vocabulary across other subjects.

The Common Core standards are being expanded to all grades next year.