Rarely, a user writes in with a question about the issue of academic honesty and the existence of Rewordify.com. Here's my response.
Creator of Rewordify.com
I was a high school English teacher for eight years, and I still work in a semi-administrative role in a large public high school. I had more than one meeting with a parent over plagiarized work that was submitted to me.
Based on my experience, I believe it's unlikely that "reworded" text will be good enough to get past a teacher. Rewordify.com is a mindless computer program that tries to replace words, but it cannot read or understand. The output often contains unexpected, obviously-wrong wording that should raise red flags with you.
Also, Rewordify.com doesn't usually change enough words to allow "reworded" text to pass online plagiarism checking software. This fact, that relatively few words are usually reworded by the site, results in the preservation of the original text's style, sentence and paragraph structure, tone, and so on. You know your students' writing and you have their writing samples. If a student were to turn in plagiarized "reworded" work, it will be instantly obvious to you that he or she didn't write it.
Before the Internet, it was virtually impossible for a teacher to prove plagiarism unless he or she visited the local library and spent lots of time reading through suspected books for suspected plagiarized passages. (Don't forget the pocketful of coins for the copier!)
The same classroom practice that combatted plagiarism back then continues to work well for me today, and will work for you, too: have your students do the bulk of their writing in the classroom, supervise your students carefully as they write, keep samples of their writing, and get to know their writing well.
Rewordify.com is used all over the world by millions of people. I have received hundreds and hundreds of emails from tremendously grateful teachers and educators because of how the site gives their students a new way to read, understand, and learn. Could an unscrupulous student be tempted to steal text, reword it, and turn it in? Maybe. For the above reasons, I don't believe it will pay off for the student.
I believe that the good the site does far, far outweighs this minor distraction.