Effective Grammar and Writing Instruction - make sure you use it properly!
A few people have said that the AI won't accept the answer when it's correct. Actually, the AI won't accept an answer if it has typos, etc. I personally love this about Quill. For instance, if the lessons is about comma placement, but a student misspells "the" (which they DO! So weird! But..."teh"), Quill won't accept the answer. I like that it forces students to pay attention to details. Far more effective than me going through and marking each and every error.
How I Use It
I assign 20 minutes of Quill practice per week for my English 10 and English 11 classes. Not only do the students seem to have fun with it, the various diagnostics and reports help me know where they're successful and where we need to build.