I previously took the gmat and scored a 640, currently I'm taking
Manhattan GMAT in order to increase my score and I'm very happy.
I view the study class as a type of personal trainer, and as with a personal trainer if you don't have a positive "win-win" attitude and come ready to rock you will not do well.
This is not to say the original poster didn't put in enough effort but I have noticed that many students in class treat the gmat as a joke. They are the late commers, those who never do their homework and those who skip class. Personally I've benefited a great deal from
manhattan gmat and am glad I signed up (I also really l like the no-nonsense instructor).
In conclusion, I would recommend
manhattan gmat but like anything else it is a tool and requires a lot of work on your part. If you are looking for a structured study plan with help, encouragement and resources check out
manhattan gmat. If you are expecting a short cut or to learn everything from showing up in class then you won't benefit.