Hi Hesham,
I just wanted to add 1 cent to the discussion. As you might know, the verbal section in the GMAT is more weighed than the Math, in other words a 22 in each section would not yield the same change in the total score. Now, within the Verbal section the SC part is extremely important. Not only is it the most learnable, the most numerous, the most time saving, but it gives a structure to the rest of the exam. When I first heard the word GMAT I had no idea how to correct sentence, I am a native speaker yet Spanish is also my first language. After doing thousands of problems, going back to basic grammar books such William Strucks - Elements of English, and The Little English Handbook by Corbett and Finkle I grasp little by little the actual meaning of the structure of a sentence. Before this, I tackled the MGMAT guide (it was super overwhelming and I probably retained 30%). Regardless, after all this, I took a class at Knewton and strengthened my SC through the eyes of a professional. I rewatched the videos 3-4 times (4 total) and I did all the SC practice problems in the OG and kept an error log in excel. All this to say, from knowing nothing and having a 35% hit rate I went to a 85% hit rate at the moment. I have gone through all the OG 11 and OG 12 SC problems, regardless of them being repeated. I have read most of the answers explanations and why the other options are usually wrong. Not only do usually I end up in a 50-50 split between two choices like you do on CR but I do this in approx 50 secs... sometimes in 1:30 if the question has many clauses, modifiers.
The essence of the story - SC is broad yet very very learnable and the learning comes from two avenues - the theory and the practice. Literally you need to do many many problems, you need to review the right answers, see if you identified the proper mistake tested (recognition is key), can you explain to me why ABC and E are all wrong for example?? B may have an ambigous pronoun, C and E their verbs are plural and dont agree with the subject, and B is wordy / awkward. This leaves as D with the best choice. Sometimes, if the question is repeated I dont just go for the answer, I go to find out - what error is being tested, why is it wrong, why are the others wrong, etc. Sometimes you dont know what a past participle is or what a gerund is so you have to google it, youtube it, and in the 20 min investment in different sources, one will give you the right one for you.
Now, all this talk about SC for what - because a real 700 testtaker (a pro- not me) can probably do these in 45 seconds or in very little time with lots of accuracy. This means that 14-16 questions in the test are done in say approx 14-16 minutes (hypothetical situation) with this time saving precious gem, they are able to do the CRs longer (have better chances of getting those 50-50 shots) and read their passages with more understanding. The gist --> every section is important in the test but SC is very important.
After having gone thru the MGMAT one time, I would go through this again after going through it again. I would also recommend doing each and every OG problem of SC in the 11th and the 12th guide. Every 10-15 problems, go to the solutions check all the answers and take note of the frequent mistakes your making, some new insight you learned, i.e. and is used for combination of elements (x,y and z), or is used for different possibilities (x,y, or z)... obviously this makes sense but now it makes much more logical sense and these types of words are critical in the structure of a sentence. The reason I suggest you do it 10-15 problems is so you can build on your understanding, so next problem set you have apriori knowledge... and so on and so forth. Then you might want to reread the MGMAT guide to solidify fundamentals. You think it is broad, you are overwhelmed? Start with a clean word document or excel grid and jot down the 8-9 categories tested - subject verb agreement, pronouns, comparisons, idioms, verb form, modifiers, parallelism. These are your main topics, now whenever you acquire a new learning or you want to jot it down just categorize it in this document... then revisit it 1 hour post doing work, 3 hours after, before sleeping (memory consolidation). You need to practice LOTS to get accustomed to it its not magic.
I think that improving your SC can boost your testing ability confidence substantially, improve your time management, your score and it can prove to you that something is learnable. This is why I find SC as a very fun part of the GMAT. Also, I do understand you can't afford a tutor, class but putting things in scope you took the exam 3 times thats 750 dollars (800, perhaps including logistics and all that)... Also, your MBA is going to be a hell of an investment (a course is only going to be 1-2% of the total cost). Additionally you are at an interesting point as I think that a 500 in your 4th score will not look good (it will look just normal, nothing special) but a 560-600 in your 4th score WILL probably look good. I mean it shows perseverance and it shows a positive change in behavior/performance- an upward trend in every test. I would surely appreciate it, although I am not in the comittee :P. There are some great discounts out there and cheap subscriptions in some cases and I think there is no substitute for the compound experience a test prep can provide you they have been solving hundreds of GMAT problems daily for years and they have been sharing their time with like minded people (students, 99th percentiles, GMAT is a big part of their daily discussion) - adding to their knowledge at a compound rate. Thus, it might be beneficial..
Best of luck and stay strong,
Jas
