I made a blackboard a few years ago as part of a woodworking demonstration, and although it never got finished properly, it is still functional. I dragged it out on the weekend as I was doing a bit more research for the upcoming toy-making course, and so let my resident expert tester have a go with it.
I still plan to make a new one, and actually finish it off this time with a shelf for holding chalk, a drink holder for the artist at work etc, but in the meantime, the current model seems a bit of a hit.
Nothing too complex in this design – corners are biscuit joined, a rebate cut in the back for the blackboard, and it is simply a sheet of MDF painted with blackboard paint that comes in a spray can. In this case, I’m using a piece of rope tied between two eye hooks to keep the sides at the right distance which keeps it from falling down.