Originally Posted by DAD22
You calculate the mean and standard deviation of the scores. Then you divide them up into classrooms by standard deviations: Everyone between -3 and -1 SD in one class, everyone in -1 to +1 SD in another, and everyone in +1 to +3 SD in the last. You are treated as equally exceptional whether you are significantly above the mean, or below.
Approximately 2/3 of standardized normally distributed samples are between -1 and 1, with 1/6 below -1 and 1/6 above 1, so your suggestion would result in the middle group (-1 to 1) having 4 times as many students as the bottom group or the top group (since 2/3 = 4*1/6).