Here is an article about grading of essays on standardized tests

http://www.nytimes.com/2012/04/23/education/robo-readers-used-to-grade-test-essays.html
Facing a Robo-Grader? Just Keep Obfuscating Mellifluously
By MICHAEL WINERIP
New York Times
April 22, 2012

My comment: essay tests as a way of measuring writing skills are as problematic as multiple choice tests. I think essay exams should be used to measure content knowledge, as the essay portions of the Advanced Placement exams do.