Miss Finster is an assistant teacher who is the children's constant nemesis on the playground. Archetypal authoritarian teacher personality, Miss Finster has a strong desire for a school in which children aren't allowed to have fun or act like children. She is feared by all the children, and is always closely followed by her teacher's pet, the equally nefarious Randall C. Weems, who is also largely disliked by the other students. In terms of inter-personal relationships, Miss Finster has been shown to have a crush on the school's janitor, Hank and is friends with Spinelli's parents. Of particular note is that she used to have a much sunnier disposition and throughout the series glimpses of this are seen with occasional references to her experiences in Guam. Despite her old age, Finster is an accomplished boxer and is generally in excellent physical condition. She keeps a punching bag in her bedroom. Former Navy commodore from 1952 to 1954. (Korean War.)
- Her surname "Finster" is the German word for "sinister".
- She is voiced by April Winchell
- She had a broken hip and phlebitis in 1983.
- She was friends with spinelli's grandmother back when she was in Guam.
- She had pink glasses and brown hair when she was younger.
- She once had phillium Benedict as her boyfriend but she broke up with him when she found out when he was taking away recess.