OG is the ultimate bible. all questions have important concepts in them which if you master should be a strong foothold.

BTG practice questions. (buy)

MGMAT SC Guide has not enough practice but is good enough for concepts.

Aristotle has a question bank. www.aristotleprep.com (buy)

egmat also has 500 plus questions. (buy)

I'd highly recommend:

1) Stick to as many official questions as you can. GMAT sentence correction is beautifully written - those authors pick perfect situations to express the particular comparisons (parallelism), timelines (verb tenses), etc. that lend themselves to great questions. And official questions are so well-edited in addition to well-written that you're not likely to end up studying things you don't need or inadvertently picking up bad habits or anything like that.

I've written some SC questions that I'm really proud of, and others that I think are serviceable. In either case, it's tough to mimic that perfect GMAT style, and I know I've seen a lot of just bad questions out there. The GMAT makes questions harder by better obscuring the logic of the question or by picking a situation that perfectly masks a necessary big-picture rule. A lot of amateur authors make questions harder by using more obscure idioms or taking other leaps that just aren't GMAT devices, so I think people get led astray with their study away from the standardized, big-picture strategies that lead to success.

2) Think before you look at the OG solutions. The OG solutions are "precise" much more so than they're "helpful". But when people read them they tend to try to think like them, so you find yourself using ambiguous terms like "unidiomatic" and "awkward and wordy" a lot more than you should. The standardized, big-picture rules are what you want to emphasize, and you'll almost always - and I use the term "almost" loosely...I mean 99.9% of the time - be able to eliminate 4 answers and pick 1 ONLY using big-picture strategies.

So use the OG and official tests for practice SC questions before you start picking them up from a whole bunch of independent sources, but focus on reputable companies' strategies instead of trying to pick up all the jargon in the OG solutions. The worst SC class I ever taught was the one in which I had the OG solutions on each page of my book and I tried to teach those instead of putting things in my own words. Halfway through that class I didn't understand SC anymore...I was losing myself by trying to teach from the official solutions. They're just not helpful, but that's not their purpose.

This link - https://www.veritasprep.com/blog/2011/04 ... orrection/ - should help set you on a path toward quality SC study. I just talked to an HBS-bound, 99th-percentile-scoring potential instructor this morning, and she echoed most of what was in that article; it wasn't until she stopped worrying and started really thinking - logically and systematically - that she felt confident on the test, and it worked out perfectly for her.

Thanks for the very helpful tips!!!