Yup, I'd be willing to bet anything that you're rushing and making silly errors.
When you look at the quant exam overview screen for your MGMAT tests, look for two things: 1) questions that took you longer than three minutes, and 2) questions that you missed that were below the 700 level, especially the ones in the 300-500 and 500-600 categories. It really doesn't take too many "unforced" errors on easier questions to absolutely demolish your quant score. It's an inevitable byproduct of adaptive tests: if you flub easier questions, you'll see a bunch more easy questions, and your score will plummet. And if you have a habit of getting stubborn on the tougher questions, that can make things even worse--you'll fall behind, feel flustered, and flub even more of the easy questions.
If it's true that you're making a handful of dumb errors on every test, then concentrate on accuracy as you practice. Make sure that you absolutely religiously spend a little bit of extra time on every quant question to make sure that you stamp out the unforced errors. Read every question twice before you start, pay close attention to easy-to-overlook modifiers (x is positive, x is an integer, x is two digits, etc.), recheck your arithmetic and algebra as you go, and spend an extra few seconds looking for traps before you click "next." It doesn't take much extra time to do all of this, and it's absolutely essential if you want to perform up to your abilities. You can always save time by punting on the particularly difficult questions.
Remember that you can miss a crapload of questions and still get an awesome GMAT quant score. You could easily miss 15-17 questions, and still get a 47 in quant. You could also miss 15-17 questions and get a 37 or a 27. You just can't miss the easy ones.
Good luck with everything!
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