The author writes that "digital tools such as iPads and Evernote provide [...] ways to efficiently capture [student] learning through a variety of techniques, including audio, images, and text," providing chances for the teacher to respond and to celebrate achievement. In general, I picture these tools working well for collecting, displaying, and promoting certain projects or getting "snapshots" of representative (or exceptional) work from a class. Digital portfolios also make it possible to connect different types of media, as the author demonstrates with his example of kids' written stories coupled with their audio reflections.
I see large issues with managing digital portfolios in middle or high school classes, however. I will probably have 160+ students next year. There is no way I could manage that many individual digital portfolios as a teacher, unless my students had the technology to keep their own portfolios under my management, which they won't. I also wonder about the practicality of putting each student's work, especially graded work, on the web without risking major FERPA issues. The author says, "It is important that the audience – the [student?], teacher, the students themselves, other staff, the parents – see the growing and culminating pieces side by side." He's a school principal, so presumably he has thought through the FERPA issues somehow, but at a middle school level I definitely foresee privacy issues with his approach.