How I Use It
I have used Dropbox with a high school media class. I shared a common folder with the entire class, and they can add pictures to that folder as they take them. This way, all students (and the teacher) have immediate access. I have also used Dropbox as a way to store pictures I want to use with an ipad app, when the pictures were taken with another camera.
Dropbox is a great utility to hold and share files you want to make available to others, from individuals to groups large and small. Although it does not really 'teach' students, it makes available resources that you want them to have easy access to. The sharing folder feature can help teachers and students share resources. The free version offers 2GB of space, which is adequate for most needs, unless you are sharing lots of pictures or videos.