Hello,
When you review practice GMAT tests, there are a few important things to consider.
1) A score can dip from one exam to another even with the same amount of knowledge ot the same percentage of correct/incorrect. The GMAT scoring algorithm takes many factors into account including where you make errors (eg making mistakes on 'graded' versus experimental questions, or the 'weight' of the question itself etc), how many mistakes you commit in a row, whether you finish both sections or leave questions out, whether the last few questions of either section seemed like they were guessed at (ie did you spend only a few seconds on the last few questions as opposed to the full time you should have), how you felt on test day - these can all affect score.
2) Use sim tests as an important tool for improving your overall test performance by practicing better time management and guessing strategies, and for learning from your mistakes. However, we suggest that you ignore the resulting score reports on any non-official practice test. The GMATPrep tests provide a decent prediction of your score (with a +/- 30 point variance due to test day conditions and pure dumb luck), which is why we recommend doing these last to get an accurate measurement of your post-prep status, but even these can be tricky.After taking a few exams you should see your range for the real test.
Good luck!
Elizabeth