The notion that the essays on the GRE are graded by computer is ridiculous. Here is what ETS has to say about it:
"Computer-Based General Test:
Your scores on the Verbal and Quantitative sections of the computer-based General Test depend on your performance on the questions given and on the number of questions answered in the time allotted.
Because both of these sections are computer-adaptive, the questions presented are selected to reflect your performance on preceding questions and the requirements of the test design. Test design factors that influence which questions are presented to you include
1. the statistical characteristics (including difficulty level) of the questions already answered
2. the required variety of question types
3. the appropriate coverage of content
For the computer-based Analytical Writing section, each essay receives a score from at least one trained reader, using a six-point holistic scale. In holistic scoring, readers are trained to assign scores on the basis of the overall quality of an essay in response to the assigned task. The essay score is then reviewed by e-rater, a computerized program developed by ETS, which is being used to monitor the human reader. If the e-rater evaluation and the human score agree, the human score is used as the final score. If they disagree by a certain amount, a second human score is obtained, and the final score is the average of the two human scores.
The final scores on the two essays are then averaged and rounded up to the nearest half-point interval. A single score is reported for the Analytical Writing section.
The primary emphasis in scoring the Analytical Writing section is on your critical thinking and analytical writing skills rather than on grammar and mechanics. (Read the Issue and Argument scoring guides.)
During the scoring process, your essay responses on the Analytical Writing section will be reviewed by ETS essay-similarity-detection software and by experienced essay readers. See Independent Intellectual Activity."
Source: http://www.ets.org/portal/site/ets/menu ... _Reporting
They are scored usually by 2 independent scorers. The scorers are most often professors, usually of writing or literature or something along that line. The scorers give a 1-6 rank of your essay, and then the two scores are averaged, which is how people are able to earn .5 scores such as 5.5, etc.
As someone currently in an Ed Psych doctoral program, I can assure you that the AW scores are not all that important in admissions decisions. The faculty are more concerned with your research interests, fit, and future goals. Ed Psych people in particular understand the problems with making admissions decisions based solely on one test score. If you have a law degree, then the ad com can see you are capable of writing. The questions then become more focused on your research interests, and how well you fit in with the department and the faculty who are accepting students.