Quick Answer
The AAMC PREview exam is scored on a 1-9 scale. Your score comes from how well your ratings align with the consensus key.
You receive full credit when your rating exactly matches the keyed rating. You can receive half credit when your rating is one step away but stays on the same side of the effective/ineffective divide, such as rating an Effective response as Very Effective. You receive no credit when your rating crosses that divide, such as rating an Ineffective response as Effective.
Your score report includes your exam date, total score, a confidence band of plus or minus 1 point, and percentile rank. The confidence band is important because it means small one-point differences should be interpreted carefully.