Which of the following is NOT required for the N-400 application?

The correct answer is that a diploma from a U.S. school is not a requirement for the N-400 application. The N-400 application, which is used to apply for U.S. citizenship, focuses on specific prerequisites that demonstrate an applicant's eligibility, such as proof of lawful permanent residency, evidence of tax payments, and proof of residence. A diploma is not among the mandatory documents; instead, the application emphasizes a confirmed immigration status and adherence to certain civic responsibilities.

While educational credentials might provide context about an applicant's background, they do not affect the fundamental eligibility for U.S. citizenship as laid out in the N-400 guidelines. Therefore, a diploma from a U.S. school is extraneous in the context of the application requirements.