It used to be that my students learned to write by writing on paper. Sometimes they wrote in notebooks and sometimes they wrote on single sheets, but no matter how they wrote, I was the intended audience. In most cases, I was the only person who ever saw that writing.
Sometimes their parents would take the time to read through their notebooks and papers as they came home or at the end of the school year. Sometimes they would read their writing aloud to the class. But in most cases, unless I posted their writing on a bulletin board in the hallway, a very limited number of people had access to that writing.
Wow! Has that changed!
Now, my students regularly write on their blogs, not just for me, but also for their parents, grandparents, other relatives, friends and potentially the whole world to see. When they write a tweet, they have the potential of all of our Twitter followers seeing what they write, and since many of our followers are classroom groups, that number is potentially far higher. Not exactly the same as writing in a notebook. Their audience now exists in places they have never been and may never visit.