The stanine method for scaling test results uses a nine-point scale with a standard deviation of two and a mean of five, and a simple algorithm involving ranking and splitting the scores helps teachers categorize their students' results in different achievement levels. In general, stanines permit teachers to obtain a sense of their own students' achievement in comparison with other groups around the region or nation, and stanines yield a meaningful average, while percentiles do not.
In order to calculate stanines for a set of test scores, rank them from bottom to top. The bottom 4 percent receive a score of 1, the next 7 percent get a 2, the next 12 percent get a 3, the next 17 percent get a 4, and the next 20 percent get a 5. Then, follow the ratios downward as you move upward from 5: the next 17 percent get a 6, the next 12 percent get a 7, the next 7 percent get an 8, and the highest 4 percent receive a 9.
Using this method allows teachers to elicit a single-digit number from any test score. SOme distortion occurs when student scores are just on the other side of a stanine boundary from one another, but overall, this is a helpful method for classifying results.