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The NAEP Science Scale

__ More Information __  • Learn more about what the assessment measures and how the answers are scored.  • Find out what students should know and be able to do in science by looking at science achievement levels.

For every subject assessed, NAEP reports on how well students in different demographic groups (e.g., 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 science, NAEP creates a scale ranging from 0-300, 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 scale, it is useful to create an "item map." An item map is a representation of the skills and abilities demonstrated by students at various levels of the NAEP science scale. The map indicates the kinds of questions students are likely to answer correctly at each level on the scale. To get a more complete sense of the science scale, take a look at these item maps for grade 4, grade 8, and grade 12.

NAEP uses the three grade-specific science scales to report on how well students in different demographic groups, such as race, gender, and region performed on the science assessment. For example, the table below compares the performance of male and female students at each of the three grades assessed.

Science Scale-Score Results by Gender: Public and Nonpublic Schools Combined         Selected Percentiles   Percentage of Students Average Scale Score 10th 25th 50th 75th 90th Grade 4 All Students 100 150 105 129 153 174 191 Male 50 153 107 132 156 177 194 Female 50 147 104 126 150 171 188 Grade 8 All Students 100 151 103 128 154 177 195 Male 51 154 105 131 157 181 199 Female 49 147 100 125 150 172 190 Grade 12 All Students 100 147 102 125 148 171 190 Male 49 148 102 125 150 173 192 Female 51 145 102 124 147 169 187 NAEP science scales were developed independently for each grade; therefore, results are not comparable across grades. Scale scores for all grades range from 0 to 300. SOURCE: National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2000 Science Assessment.

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Last updated 3 March 2004 (CC)