I have been using Evernote (iPad, Mac PC))for about 5 years off and on. However, I made it my go to note app about 2 years ago and haven't looked back. I believe that Evernote is a great tool for tracking student progress. Evernote allows typed notes, handwritten notes, images, and even audio recording. There are other apps that Evernote can sync with that provide an even broader use of the Evernote platform. My two favorite are Skitch (iPad, Mac), (allows you to annotate on photos) and Penultimate (allows handwritten note, drawings etc.). These apps have been purchased by Evernote over the past two years allowing for great integration with Evernote.
One of the other reasons that I love Evernote is that it is available over most computing platforms and it syncs very well between them all. That means that as I create and add to notes on my iPad, that information is automatically synched to my Evernote on my laptop and on the web. To me the ever in Evernote means everywhere which is where my notes end up. I can access those notes from any devices.
This means that a teacher could be working with a small group in language arts for example and as they are working with the group and students are reading out loud, the teacher could not only take written notes, but record the student reading, all in Evernote. There are many such uses for Evernote. For more information on general use of Evernote, you can visit their tutorials at http://evernote.com/evernote/guide/mac/
Teacher Nicholas Provenzano used Evernote heavily in his classroom last year and detailed that experience at http://www.thenerdyteacher.com/p/the-epic-evernote-experiment.html
Here is a brief video showing a few of the things that Evernote can do.