Originally Posted by Bostonian
To some extent the poor writing may be the result of poor teaching in K-12, but I think the primary cause is low intelligence in many students. About 1/6 of the population has IQ <= 85, and the writing samples may illustrate the thinking and writing that the left tail of the bell curve is capable of.

Low IQ would explain some of the poor writing, but it wouldn't explain the grading.