Since I was wake at 5 AM on a Saturday (don't ask), I figured it was a good time to update my Personal Learning Network on Twitter. For years, I've been saying Twitter is the best free professional development tool available; I even teach an online course at two colleges on the subject.

Not familiar with the power of Twitter? You doubt the veracity of my proclamation? Check out the amazing PD and personal enrichment I got on an early Saturday morning.

With the intention of growing my PLN, I went to one of my favorite educators, Shelly Terrell. One of the most energetic and brilliant teachers I know (by the way, I met Shelly on Twitter and later at the ISTE conference), I know she follows remarkable people in education, business, leadership and entrepreneurship, so I figured I couldn't go wrong following some of the people in Shelly's PLN.

Soon, I found Jordan Hamel, an engineering student, who is working on an education technology app. Since I recently launched a mobile app of my own, I reached out to Jordan so we could connect and share ideas.

Next, I found Jeff Herb, an Instructional Technology Director at a high school in Illinois. Jeff's Twitter profile led me to his web site, Instructional Tech Talk, a veritable treasure trove of technology resources. Jeff's site guided me to an article about the educational tool, eBackpack, a site that provides an online storage area where students can easily maintain and organize activities.

Next, I found Roxanna Elden, a teacher and writer. Her Twitter profile routed me to a website that describes her book, See Me After Class. I read a review by Education Week, which said Elden's book has "a heavy dose of practicality, a dash of cynicism, and wry humor." I was intrigued and moments later, I was on Amazon.com downloading See Me After Class to my Kindle.

In about 45 minutes of perusing the Twitter PLN of one of my favorite teachers, I found an educator with a common interest, an edtech teacher who edits a powerful website, and I discovered a new online tool I may wish to use with my own students. Oh, and I found a new author and added an education book to my library.

By the way, all of this was free professional developmet (although I did purchase Elden's book).

I could have attended a day-long workshop, which would have cost hundreds of dollars and consumed my entire Saturday. The learning would have been negligible. Instead, I spent a wonderful 45 minutes in the comforts of my own home, sipping hot coffee, and I learned more than I have in the last five workshops I've attended.

So, you see, if you're not using Twitter, you're missing out on the best free education PD, period!

Learn more about Twitter today.

Mark's new book, Role Reversal: Achieving Uncommonly Excellent Results in the Student-Centered Classroom is available for preorder from ASCD here.