A behavior analyst is conducting research on the accuracy of a student's responding to written math problems based on the final answer with no scoring of intermediate calculations. Which is the BEST method for obtaining accurate inter-observer agreement results?

Researcher and observer sit together to score the student's work.

Photocopies of the student's work are scored independently by researcher and observer.

The student's scratch paper is scored if researcher and observer do not agree on a response.

Researcher scores the student's work and the observer reviews the researcher's scores to accuracy.