For multiple choice and fill-in-the-blank assignments and tests, the most popular answer key format is two or three columns, starting on the left side of the paper and going down. Some teachers use programs such as Microsoft Excel to create a table with a similar layout.
Using columns to grade tests and assignments makes grading quicker and easier. Teachers can line up the answer key next to the answers on the assignment for a quick check of answers.
This format does not work for essay questions, as those need to be read in their entirety. Having an answer key with the question and answer below it to compare to the student's answer is preferable.