NOTE: The arrowheads point to samples for which assessment results were already in the NAEP reporting metric in preparation for the 2013 mathematics assessment. The 2011 to 2009 concurrent calibration was conducted previously and is only shown here for completeness. 
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2013 Mathematics Assessment.