Reading Ability Scale
With an adaptive test, students within a class answer different questions depending on their abilities. Weaker students attempt easier questions whereas more able students attempt harder questions. Therefore a weaker or a more able student may get the same number of questions correct but they will have different abilities. The ability scale score takes into account the difficulty of the questions a student has attempted and is the adaptive equivalent to the raw score for a static test. Any use of raw scores in a fixed test applies to the ability scale. The advantage with the NGRT scale score is that you can use it to track the absolute Reading ability of an individual over time. SAS scores are adjusted for age and the average SAS score at any age group nationally is 100.
The chart and table below shows the percentile distribution of the scale score by age. It shows that the average (50th percentile) scale score for students at age 7 is 228 and increases to 342 at age 12. The top 10% of students (i.e. 90th percentile) at age 7 have a scale score of 308 or higher and at age 12 the top 10% of students have a scale score of 400 or higher.