You should not attempt to explain this in the optional essay. The fact of the matter is that you cannot explain away a poor performance. I'll be honest with you – it looks incredibly lame. I do not mean any disrespect, I just want to prevent you from doing something that will waste the admissions committees time.
You do not exist in a vacuum. There are plenty of other applicants out there with poor GMAT scores. What if every single applicant to Stanford or Harvard tried to justify some sort of poor performance in the optional essay? Everyone thinks that they have a good or unique rationale, but the reality is that no one does. The GMAT is the most important factor in the admissions process because it is really the only apples to apples comparison that the admissions committee will have. It really is a good test of your aptitude. To be clear, this is not to be confused with your potential or your contributions to society or even your chances at LBS.
Now let's look at this another way. Think of all the other applicants that will share a similar profile. While I would like to think that I myself am a unique snowflake, I know that I am not. In the same way, none of us really are. So what am I saying? I am trying to make the point that there will be someone else applying with a similar background to yours. Heck, they might even have a name very similar to yours as well -- let's call him jimmychu. However, they will not have a deficient score on the verbal section of the GMAT. When the adcom looks at your score (and your explanation), as well as jimmychu's, they will see that his score is much more equitable and well -- higher. They won't really pay attention to your written explanation -- which would basically amount to "a dog ate my homework" explanation.
So again, do not write up an explanation stating why your verbal is so low. If the GMAT verbal is not reflective of your grammar skills, then a 100 word explanation is not sufficient. Spend the time studying the verbal section of the GMAT instead.
I hope I do not sound harsh, but its crunch time and you need to go in armed to succeed and not fail. Consider re-taking the GMAT.
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