| Character Description | Character |
| A scrawny, red-headed boy in Arnold's class who is both geeky and optimistic. | |
| Said character's father. | |
| A somewhat paranoid boy in Arnold's class who always wears a green hat backwards. | |
| An incredibly psychotic boy in Arnold's class who wears glasses and has a bowl haircut. | |
| A nerdy girl in Arnold's class who is friends with Eugene and hates violence. | |
| A 'cool' girl in Arnold's class; best friends with Clue 25. | |
| A Korean American boy in Arnold's class. | |
| A boy who continually stalks Clue 18 and is known for constantly breathing deeply and getting his glasses broken. | |
| A Hispanic American boy in Arnold's class who is incredibly rich. | |
| A resident bully of Arnold's class whom Arnold tutors in math. | |
| A younger boy completely obsessed with chocolate. | |
| The 5th Grade bully of the show; loves picking on Arnold and his friends; not terribly bright. | |
| Said character's sidekick. | |
| A suspicious looking 5th grader who deals in all the shady businesses of the school (e.g. following someone to enforce the rules of a bet.) | |
| A very pretty 6th grade girl, whom Arnold has a crush on. | |
| A very mean and annoyed 6th grade girl whom Clue 15 is friends with. | |
| Arnold's first 4th grade teacher; an optimistic, cheery woman with gray hair. | |
| Arnold's second 4th grade teacher; a former drill sergeant and very strict military man. | |
| Arnold's third 4th grade teacher; the nicest, nerdiest and most sensitive teacher to his students. | |
| The principal of Arnold's school. | |
| The school coach; often gets Arnold and his friends to join different teams. | |
| A local butcher who ends up becoming a politician. | |
| A poor man who fights crime on the streets and has a huge fascination with monkeys. | |
| A quiet man who prefers the company of pigeons to people. | |
| A kid who was known for never leaving his favorite spot. | |
| The unfriendly, slightly deranged driver of the Jolly Ollie Ice Cream truck. | |