Since you have been studying for the GMAT for over a year without much improvement, there must be a fundamental issue in how you have been studying. I see you have used a number of different resources to prep for the GMAT; however, when using these resources have you been able to achieve linear and targeted learning? In other words, have you been able to master one topic before you move to the next? If not, you must follow that method of learning and practice to develop GMAT mastery.
For example, when learning about critical reasoning, attempt to master all aspects of critical reasoning, including the question types, before moving on to another section. Follow up your learning with focused critical reasoning practice, so you can determine your specific weaknesses within each topic. For example, if you continually have trouble with strengthening arguments based on scientific evidence, you will want to identify and overcome that difficulty. You should follow a similar routine for sentence correction and reading comprehension and also for the quant section.
Failure to achieve this type of learning and practice could be the reason why you have been unable to increase your GMAT score since last year. So, before doing any more random practice, I suggest finding a study resource that will allow you to gain complete coverage and mastery of each GMAT topic, and practice just that topic until it sticks.
Lastly, you must keep in mind that GMAT success does not happen overnight. You might have to study for longer than one month in order to raise your GMAT score to a 650+. Thus, you might consider taking your GMAT at a later date and also consider applying to school in round 2.
But - don’t give up!!! You can make this happen!!
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