From a post titled Education Data Mining and Visualization by David Wiley at BYU:
The first visualization we’ve developed is one we call the “Waterfall.” The vertical axis represents students’ final grades (higher final grades at the top). The horizontal axis represents time, with each cell representing a day in the semester. Each individual row represents an individual student. Finally, the darkness of the water droplet represents the amount of time that student spent that day completing gradable activities.The result is a lot of information on a specific measure densely packaged into a single glance.
The correlation between time spent (effort, in other words) and final grade is clearly evident but there's another interesting part of the chart. Around 75% to 85% final grade there's a band which seems to put in consistently less effort overall than the clusters of students above and below it, yet still result in a decent grade. I wonder what characteristics those students possess and whether there are any patterns in the paths their lives then take.