Sketchlot is a free collaborative whiteboard service that works on any device that will work on a Chromebook, iPad, Android tablet, or any computer connected to the web. Sketchlot is designed for teacher and student use. Teachers create their own accounts and then inside that account they can create a list of students. Each student is assigned his or her own password to use to join a drawing shared by his or her teacher. Teachers can create as many drawings as they like and share them on an individual basis. Teachers can share their drawings to one or all of their students at a time. Students can create their own sketches to share back to their teachers through Sketchlot.
In the video embedded below I provide a demonstration of how to create and manage a Sketchlot account.