Race to the bottom
The report is called Mapping 2005 State Proficiency Standards Onto the NAEP Scales, and compares the proficiency scores of state tests against those of the National Assessment of Educational Progress, or NAEP (known colloquially as the Nation's Report Card).
Here's the comparison in 4th grade reading:
As you can see, a "proficient" rating on the tests of most states falls at or below even the "basic" ranking on the NAEP (and in some cases, far below).
Using Tennessee as an example, this explains why we see an average K-8 proficient/advanced score of 88% in math as reported by the state, while far fewer of those same students show up as proficient or advanced on the NAEP math assessment: specifically, 31% proficient/advanced in 4th grade, and 24% in 8th grade (click here and go to Tennessee).
As Ken notes in his post, it's a race to the bottom: in order to trick citizens into thinking their schools are performing well, states are watering down their tests to increase pass rates. If we keep this up, in the words of Stephen Colbert, we'll get to the point where passing the math test means you move when poked by a stick, and passing the reading test means that your breath fogs a mirror.
Is this really what we want?