More detailed information about what students know and can do in
each subject area can be gained by examining their attainment of
specific performance levels in each assessment year. This
process of developing the performance-level descriptions is
different from that used to develop achievement-level
descriptions in the main NAEP reports. For each of the subject
area scales, performance levels were set at 50-point increments
from 150 through 350. The five performance levels—150, 200, 250,
300, and 350—were then described in terms of the knowledge and
skills likely to be demonstrated by students who reached each
level. A "scale anchoring" process was used to define what it
means to score in each of these levels. NAEP's scale anchoring
follows an empirical procedure whereby the scaled assessment
results are analyzed to delineate sets of questions that
discriminate between adjacent performance levels on the scales.
To develop these descriptions, assessment questions were
identified that students at a particular