I'm just starting Week 3 of the Knewton course. It's a live online class which is completely flexible, and I can change sections whenever I need to, or watch a stored class.
I scored a 570 on the pre-course Practice GMAT. Pretty good, considering that I had done zero prep work at that point. We haven't taken another Practice GMAT in class yet, but I can tell that after only four classes I've gained skills that will bump my score up. I'm already much more comfortable with the questions, and I rarely have that "where the heck do I start?" moment any more.
I beg to differ with people who think running through practice tests is good enough. I thought the same thing before starting this course. I do well with independent study, so I wavered on taking an actual course. After four classes I'm already happy that I invested the money. The Knewton instructors all have top GMAT scores, and that insight is invaluable.
I obviously can't tell how my Knewton GMAT score compares to the real thing, but they've hired two of the people who developed the original GMAT CAT algorithm.
BTW - if you plan to sign up for the Knewton course, keep an eye out on their website, since they often offer $100 off. I got $100 of my course on the last day of the offer, and a few days later they had a different discount which included 1200 extra practice questions. The ONE TIME that procrastination would have paid off for me.

Dinah S.