Zero

Hector Zeroni (Zero): The deuteragonist and Stanley's closest friend. He is the smallest, quietest boy in the camp who is unfairly labeled as unintelligent until Stanley teaches him to read.

Mrs. Walker

The Warden (Ms. Walker): The primary antagonist. The cruel, manipulative boss of Camp Green Lake who forces the boys to dig holes under the guise of "building character," when she is really searching for buried loot.

Mr. Sir

Mr. Sir (Marion Sevillo): A mean, antagonistic counselor who wears a cowboy hat, chews sunflower seeds, and oversees the boys while carrying a gun.

Mr. Pendanski -mom

Mr. Pendanski (Mom): The counselor of Tent D. He seems friendly and understanding at first but is ultimately sarcastic and emotionally abusive toward the boys.

Twitch

Twitch (Brian): A nervous boy sent to Camp Green Lake late in the story for stealing cars. He constantly fidgets and takes over Zero’s empty cot after he runs away.

Zigzag

Zigzag (Ricky): The most eccentric and unpredictable boy in the tent. He has frizzy hair, easily loses his temper, and accidentally hits Stanley with a shovel.

Magnet

Magnet (José): A camper with a talent for stealing. He gets his nickname because his fingers act "like magnets" when he steals Mr. Sir's sunflower seeds.

Armpit

Armpit (Theodore Johnson): One of X-Ray's closest allies. He is large, physically intimidating, and later becomes the main character of the sequel book, Small Steps.

X-Ray

X-Ray (Rex Washburn): The unofficial leader of Tent D. He wears thick glasses, decides the social order, and claims Stanley's discovery to get the day off.