National Center for Education Statistics [PDF]
There is wide variation among state proficiency standards.
• In 2009, as in 2003, 2005, and 2007, using NAEP as common metric, standards for proficient performance in reading and mathematics varied across states in terms of the levels of achievement required. For example, for grade 4 reading, the difference in the level required for proficient performance between the five states with the highest standards and the
five with the lowest standards was comparable to the difference between Basic and Proficient performance on NAEP. The results for reading at grade 8 and mathematics in both grades were similar.