|Abilities||Flight, super-speed, super-strength, super-hearing, enhanced mathematical knowledge|
|Voice Actor||Jack McBrayer|
He is voiced by Jack McBrayer.
He first met Wordgirl when she was battling Doctor Two-Brains.
He has dark brown hair that stands straight up and a square face. He wears glasses in and out of costume. He is shorter than most kids in the fifth grade.
As Kid Math, he wears a bright cyan outfit with white gloves and boots, a yellow utility belt, and a symbol on his chest: a cyan equals sign on a white circle.
As Rex, he wears a red hoodie, teal shorts and.sneakers. His Kid Math costume is visible underneath.
He thinks things through logically, possibly due to his Hexagonian origins. He is new to being a superhero, and messes up sometimes, though he is eager to get better. He seemed to have difficulty with moral comprehension in the past, as evidenced by him suggesting he and Wordgirl destroy Fair City in order to stop Dr. Two-Brains' evil plan. Since then he's learned to value feelings as much as logic.
- He is one of the only characters to figure out Wordgirl's secret identity, the others being Tobey (temporarily), Dr. Two Brains (also temporarily), Scoops, Violet and Bampy. Part 2 of the episode that's about him show that he has a crush on Violet.