Answer :
"After the assembly, the principal of the class, Mr. Fulton, asked the students to calmly leave the auditorium" is correct. If the assembly was referring to a specific event titled "The Assembly", then assembly would be capitalized. And "principal" is not capitalized because it's not being used in a proper title.
Answer: After the assembly, the principal of the class, Mr. Fulton, asked the students to calmly leave the auditorium and move into the lunchroom.
Explanation: The principal's name should be capitalized, but his title shouldn't be capitalized unless it comes before his whole name as in "Principal Mike Fulton." Since the auditorium and lunchrooms aren't named after anyone, they don't need to be capitalized.