I have taken 2 practice GMATs thus far, one GMATPrep and one MGMAT. On both exams, more than half of my incorrect Verbal questions were Sentence Correction. On the MGMAT, specifically, I answered 6/15 SC correct. However, MGMAT told me that all but 1 of those 15 questions were 700-800 difficulty, thanks to my good scoring in RC and CR which raised the difficulty for the Verbal section as a whole.

That being said, it was obvious I needed help in the SC department.

I completed the entire 113 questions in the OG Verbal Supplement 2nd edition (blue). They are supposedly given in order of difficulty. Here are my results:

1-30: 83.3% correct
31-60: 83.3% correct
61-90: 70% correct
91-113: 70% correct

I sincerely don't believe I've improved from a 6/15 (40%) on my practice exam to a 70% of the highest difficulty, as I've only been practicing solely on SC for 2 study days.

Does the highest level of difficulty for SC in the OG books rival that of the highest difficulty on the actual GMAT exam? I don't want a false sense of confidence going into my test (2 weeks) only to be faced with SC questions more difficult than I've practiced. My RC and CR are very strong, so I know I will be getting difficult SC questions. As my % correct above indicate, I have no problem with easy to medium and even relatively hard questions. Should I be using another source to test my SC skills?