<p>The difficulty of each question is known quite well before it appears on a test, since each question on the SAT is tested for difficulty and appropriateness when it appears in an ungraded (equating) section. (For example, questions that are too hard or too easy are “inappropriate”.) Every question goes through this process.</p>
<p>But the difficulty of the entirety of a test form is unknown until it is administered. How items are arranged, exactly what topics are covered, etc. can affect the difficulty of the test as a whole.</p>