The Flesch-Kincaid score tells you the readability of this essay. A higher score is easier to read.
Here is the breakdown:
90 to 100 - 5th grade
80 to 90 - 6th grade
70 to 80 - 7th grade
60 to 70 - 8th and 9th grade
50 to 60 - 10th and 12th grade (high school)
30 to 50 - college
0 to 30 - college graduate
For more information, visit the Wikipedia.