Are GRE practice test scores accurate? / Do they predict the real score?

Official ETS PowerPrep Plus practice test scores are highly predictive of your real GRE score, assuming similar conditions and performance. Since these scores are not an objective measure (like your height) that would be the same each time you measure it, there still can be some meaningful score variation between attempts (whether both are PowerPrep Plus exams, or both are actual, or some mix of the two), even if your level of preparation hasn't changed.

ETS publishes the Standard Error of Measurement (SEM) for the GRE: about 2.6 points on quant and a similar margin on verbal. That means if you score a 153 on quant, your "true score" is probably somewhere between 150 and 156 (68% confidence), or 148 to 158 (95% confidence). In practical terms, a 2-3 point swing between attempts is normal statistical noise, not evidence that your ability changed. Score differences of less than about 4 points between two test-takers on quant may not reflect a real difference in ability at all.

Sometimes people just have better days or worse days. But over years of seeing thousands of student results, most people are able to get a score at or above their practice score level, though not always on their first attempt. In addition to the natural variation already mentioned, some people just struggle to stay in the same mindset and implement the same strategies on test day, particularly on their first attempt. For this reason, we always recommend that you plan to leave time for multiple attempts just in case the first attempt doesn't go as expected.