Are you looking for students who are reflective about the quality of their work and can articulate their areas of strength and next steps?
Do you want students to demonstrate curiosity about academic content?
Are you looking for students who show perseverance and utilize various strategies in solving problems?
I would agree with all of these and yet I recently found some less formal evidence of student ownership of learning that bears noting.
The first student I came across, during Independent Reading time, was reading on Wattpad. Of course, the 6th grader had to explain to this neophyte that Wattpad was an organic community of readers and writers who submit stories and read stories form other self publishers. While the nature of this social literary community requires monitoring and guidance so students use discretion and engage safely, I was surprised to find that this student (I later found a few others) had discovered a literary community where they could read stories of interest and submit their own for the eyes of a wider audience. This same student indicated that she had some writing she wanted to share but hadn't gotten the courage to publish quite yet. Her classmate then chimed in and encouraged her to take the plunge.
My second discovery that same day was in another 6th grade class where I found a young man writing a narrative in Google Docs. I figured he was working on an assigned piece from his teacher, but soon discovered that he was writing a story of his own choosing collaboratively with a classmate (who waved at me from across the room). They had taken this collaborative tool and repurposed it for their own personal writing project.
I can think of no better evidence for students who have taken ownership of their learning then to see them choosing literacy activities, with enthusiasm, outside the school curriculum. Of course, we will continue to look for formal evidence of student ownership of learning, but these anecdotal and personal examples are evidence just as surely, and should be encouraged and celebrated in your school, as they will be in ours.