Hi Nomad48,
The scoring algorithm on the Official GMAT is far more complicated than most people realize. Since that algorithm is proprietary, no GMAT company has an exact match for it, thus CAT scores can vary a bit based on the 'biases' involved in their respective designs. In addition, there are a variety of factors that can influence your performance on your practice CATs that have nothing to do with the 'brand' of CAT that you are using (including the time of day you take your test, how well-rested you are, the environment that you take the test in, etc.). You might have just had a 'bad day' when you took this most recent CAT, or maybe it wasn't a particularly realistic Exam... or maybe you got a bit lucky when you scored 660 a couple of weeks ago (and this 570 is actually closer to your current 'ability level'). We won't know for sure until we define your prior work in more detail.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
1) What type of study routine have you been following? How many hours do you typically study each week?
2) What study materials have you used so far? What “brands” of CATs/mocks have you used?
3) On what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
4) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich