Local norms are created from the distribution of standard age scores for a particular group (e.g., school or school system) that are scored at the same time. Standard age scores use the power of national norms to control for the effects of age. If all students tested were in the same grade and tested at approximately the same time, then the effects of grade are also controlled.

In some school systems, the characteristics of the student population differ markedly from those of a national sample of school-aged children. When national norms are used in these school systems, the scores of students on both achievement and ability tests are likely to be skewed toward the high or low extremes of the score distribution. For example, some schools draw the major part of their student body from homes where the parental levels of education are very high. In schools like these, scores based on national norms for both achievement and ability tests are likely to cluster in the above-average range so that only limited discriminations can be made in the relative standings of students. In such schools, local percentile norms provide a useful addition to national norms for making educational decisions.

Students with the highest SAS in the local norm group are assigned the highest local percentile rank; those with the lowest SAS in the norm group are given the lowest percentile rank. These local percentile ranks will be the same as the national percentile ranks only if the mean and standard deviation of standard age scores in each grade equal the national mean of 100 and standard deviation of 16.

For more information on local norms, you can review A Deeper Dive into Local Norms, written by CogAT author Dr. Joni. M Lakin.