How I Use It
I introduce paperrater.com to all my students along with grammarly. I make sure to tell them that for some people, punctuation and spelling come easily. For others, however, either one of those skills can be tough and using a tool to improve shows determination rather than weakness.
After our first writing assignment of the year, I do goal setting meetings with students. For some, they self-select improving in writing conventions as a goal and for others it is something I push. By middle school, most students are aware whether or not they struggle with writing conventions, so for most students who struggle, they select the goal themselves. For those students, using grammarly or paperrater to review their work is a mutually agreed upon requirement before submitting final drafts (and is reflected in their assessment rubrics).
Paperrater is not perfect, but it sure helps some students. My students liked it better than grammarly, saying that it was more useful and easier to understand the site's feedback.
It can help catch stray errors for anyone, but its real value is in helping people who really struggle with writing conventions.