Final answer:
In 'Because of Mr. Terupt,' Jeffrey is the boy from the Collaborative Classroom known for his exceptional counting and mathematical abilities.
Step-by-step explanation:
In the book Because of Mr. Terupt, the name of the boy who can count really well from the Collaborative Classroom is Jeffrey. Jeffrey is known for his mathematical abilities and is one of the seven narrators in the novel. These narrators each have unique characteristics and issues, and together their stories interweave to form the plot centered around their teacher, Mr. Terupt.