If you are lucky enough to have access to TurnItIn at your college, I bet you didn't know it can do more than just give you a similarity rating?
TurnItIn now has e-rater, a grammar checker, that works alongside the plagiarism checker. If you don't have TurnItIn at your school, it is available for a fee online at Writecheck.com.
In addition to checking quoted, paraphrased, or summarized material, e-rater looks at grammar, style, mechanics, usage and spelling. Errors are flagged and offer students the option of dismissing e-raters' advice, or clicking on "handbook" for further explanation.
Using e-rater will improve your grammar. As a professor, I know most grammar mistakes are really proofreading errors, but when you run across something truly perplexing, e-rater's grammar handbook can teach you something new.
Before you charge off to TurnItIn with your next paper watch the following demo explaining how it works (the demo is for WriteCheck, but it works like TurnItIn).
Do your professors a favor and use e-rater to correct your grammar. Believe me, you'll be glad you did!