The abbreviation takes the form of XY where X is:

• D for danshi/男子 (boys) or
• J for joshi/女子 (girls)

And Y is:

• S for shougakusei/小学生 (elementary schooler) or
• C for chuugakusei/中学生 (middle schooler) or
• K for koukousei/高校生 (high schooler)