When my students submit a draft, I ask them to give me some areas of particular growth that they’d like my feedback on. Here, a couple of my comments in response to a student:
After reading her draft: I would like to see your writing become more sophisticated. I think one place to start is with sentence variety and sentence length. You have lots of choppy sentences that are just…boring. From this draft, I can tell you can write. Now, you have to push your limits. Go.
She asked, “Can you detect my voice in my essay?” [Side note: what a brilliant, BRILLIANT question from such a young writer. My heart, my smile…VOICE?! Remind me to write about what Keith Gilyard said about voice that made everything crystal clear-ish to me about that].
Me: It’s there, hidden underneath some dry language. You actually have a voice that is quite poetic. You’ll develop it this term. It will be fun.
Indeed, it will be–and is–fun. I needed a reminder of the joy I have working with my students. March attempts to wring it from me as it marches forth (ha), but there is such joy in this work…
Dr. Kimberly N. Parker 
Your students are made of tougher stuff than me! If my teacher had ever told me my prose was boring, I would have been really upset, lol. Then again, it probably would have pushed me to try much harder.
Yes, Michelle! The context, which I probably should have added, was that this particular student and I have a solid working relationship. She’s brutally honest with me (um, what were you trying to teach us with that lesson? It didn’t work, etc.), and responds with same. A less confident writer, though? Oh no. That would shut them right down. But I do tell them, generally, that essay voice=boring voice, but that they can and will develop other voices. Thanks!