1. A computer-implemented method of grading an essay, the essay being a response to a test prompt, comprising: deriving a set of predetermined features from the essay with a computer system, wherein the predetermined features comprise one or more features that are independent from the test prompt; evaluating the feature set with a scoring equation with the computer system; generating a raw score for the essay from the scoring equation with the computer system; and processing the raw score for the essay with the computer system, wherein an adaptive cutoff algorithm is utilized to assign the raw score to a score category, the adaptive cutoff algorithm comprising: collecting raw scored essays across all score categories, wherein the raw scored essays are graded by the automated deriving, evaluating, and generating steps and by human graders following scoring rubrics; determining an appropriate cutoff value set by maximizing an overall exact agreement between the automated grades and the human grades and a minimum lowest exact agreement between the automated grades and the human grades in a score category; and comparing the raw score generated by the deriving, evaluating, and generating steps to the selected cutoff set to obtain a score category for the essay.