This is very impressive. However, I think the essay was poorly written. The point of the essay is not just to highlight your talents, but also to present yourself in a coherent manner. I feel like you focused a lot on the coding aspect and half-cooked the writing, which happens all too often in this industry. Nevertheless, good job on the project; you got an early start on a bright future.
In the last 5-7 years, the English curriculum in US schools has changed significantly in an effort to improve NCLB reading scores. One part of the curriculum that had to get trimmed down was writing composition.
These days, unless you were home schooled or attended grades 9-12 at a quality private school, you probably won't be taught how to write a proper essay until college.