- "I'm not a little kid anymore, understand? So from now on, butt out!"
- —J.B. Slater to A.C. Slater
J.B. Slater is A.C. Slater's younger sister
She is a strong independent woman, who knows that her older brother has her best interests at heart but gets annoyed when he becomes overbearing and controlling over her life, especially when she starts dating Zack Morris.
Grew up as a military Brat, traveling the world with her dad & brother. Spent her 10th grade at boarding school, then went to Europe for the summer.
J.B. shows up suddenly to visit A.C. and Zack develops a crush on her. This makes A.C. angry as he knows how big of a womanizer Zack is, and forbids them from seeing each other. Once J.B. learns of this, she confronts Slater angrily and tells him to butt out of her love life. Slater eventually realizes that it is wrong to control his sister's life and gives his blessing, but still privately confronts Zack that he expects nothing but gentlemanly behavior when with her, or "you must treat her right".
- J.B. and her brother A.C. Slater, have initials they use for first names, though unlike her brother, it is never revealed what her initials stand for.