It's been a year since I used Knewton, but I remember thinking that the scoring algorithm on its tests was wrong. Several times, I would miss only 2-3 questions and get a lousy Q45. I e-mailed them about this, and they denied that it was flawed, but I never believed it.
I really think that Knewton is great, but I believe that its algorithm is slightly off. So don't get too obsessed with the score. You'll likely score higher on the real test than you do on the practice CATs.
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