This tool allows users to upload their written work and have it evaluated. It includes some basic grammar and spelling tools like you'd expect from a word processor but has additional tools as well. I does things like identifying: words used in correctly, overused words, redundant words, and rambling sentences and reports on readability, sentence length, pronouns as well as a number of other factors that influence the quality of your work.
Cost: Free trial version and a pay for use version.
Grade appropriateness: I haven't used this in the field but I'm thinking it's more of a middle and high school tool.