For every subject assessed, NAEP reports on how well students in different demographic groups (such as race, gender, and region) perform on the assessment. NAEP does not report individual student scores. How does NAEP summarize what students in these groups know and can do, and make comparisons among the achievement of these groups of students?
In writing, NAEP creates a scale ranging from 0 to 300, based on statistical procedures called Item Response Theory (IRT). IRT is a set of statistical procedures useful in summarizing student performance across a collection of test exercises requiring similar knowledge and skills. All NAEP subject area scales are produced using these procedures.
To give meaning to the levels of the writing scale, it is useful to create an item map. An item map is representation of the skills and abilities demonstrated by students at various levels of the NAEP writing scale. The map shows, for each level on the scoring guide, the scale score attained by students who had a 65 percent probability of attaining that level or higher for the selected prompt.