The LSAT diagnostic exam is a practice exam that is taken before the actual exam to determine where your score falls on the scale. The LSAT diagnostic test has a similar average to the LSAT test. As a result, the LSAT diagnostic test average is 151 on a scale of 120 to 180, which places it in the 50th percentile. A person must typically answer roughly 57 accurate answers in the test to achieve an average of 151.