DDS
Classes in DDS are based on the entrance test score, with A as the highest, B as the next lower, etc. It is possible for a student to be transferred to a higher or lower class, depending on their academic performances. However, Class Q is a special case. As the name might suggest, Class Q is for the Qualified students (i.e. the specially chosen few) who are viewed as the most potential candidates for the successor of Morihiko Dan in the future. Yet, the same rules as the other classes also apply to Class Q. Any member of Class Q may be transferred to a lower class if his/her academic performance declines. Since Class A was generally regarded as the top class of the DDS before Class Q was formed, there has been a tense rivalry between the two classes since.
Read more about this topic: Detective School Q, Characters