One of the students whose work I'm grading has just handed in a piece of work which is much better than what I've come to expect of them after several classes. I was just about to write some rather positive comment on their work, along the lines of "Good job! You're doing much better than you used to.", when it struck me that perhaps this is not such a great idea after all.
The problem is that, even after the jump in performance, the student is by far not the brightest in the group (not that they're not bright; the group is simply very strong overall). This leaves me with a couple of possible concerns. Maybe that would be somewhat unfair to the other students, who usually perform at a consistent level. More importantly, this might come across as a backhanded compliment. Something along the lines of "Well done, you are now about average, which is very high, judging by your abilities." (which of course is very far from what I mean to convey). Are these legitimate concerns?
On the other hand, it feels slightly wrong not to acknowledge improvement. And I usually try to leave some kind word next to a particularly good solutions of people at the top of the group.
So, is it a good idea to comment on the fact that student is doing better? If so, how do I make sure I will not be misunderstood?