US Department of Education, via a kind Chan Stroman email:

State-level National Assessment of Educational Progress (NAEP) results are an important resource for policymakers and other stakeholders responsible for making sense of and acting on state assessment results. Since 2003, the National Center for Education Statistics (NCES) has supported research that focuses on comparing NAEP and state proficiency standards. By showing where states’ standards lie on the NAEP scale, the mapping analyses offer several important contributions. First, they allow each state to compare the stringency of its criteria for proficiency with that of other states.
Second, mapping analyses inform a state whether the rigor of its standards, as represented by the NAEP scale equivalent of the state’s standard, changed over time. (A state’s NAEP scale equivalent is the score on the NAEP scale at which the percentage of students in a state’s NAEP sample who score at or above that value matches the percentage of students in the state who score proficient or higher on the state assessment.) Significant differences in NAEP scale equivalents might reflect changes in state assessments and standards or changes in policies or practices that occurred between the years. Finally, when key aspects of a state’s assessment or standards remain the same, these mapping analyses allow NAEP to substantiate state-reported changes in student achievement.
The following are the research questions and the key findings regarding state proficiency standards, as they are measured on the NAEP scale.

Wisconsin’s oft criticized WKCE vis a vis NAEP:
WKCE “proficient” = 2009 NAEP Below Basic for grade 4 reading (along with 34 other states) and grade 8 reading (along with 15 other states)
= 2009 NAEP Basic for grade 4 math (along with 41 other states) and grade 8 (along with 35 other states)
WKCE results showed more positive changes than NAEP results for grade 4
reading from 2007 to 2009, grade 4 math from 2007 to 2009, and grade 4 math from 2005 to 2009
NAEP results showed more positive changes than WKCE results in grade 8
reading from 2005 to 2009.
How does Wisconsin compare? Learn more, here.