Chalk pens work best on a glass/similar surface, we have some and let the kids doodle on our French doors. If you are going to do a blackboard on a wall could you put a little shelf along the bottom like on traditional blackboards to catch the chalk dust?
I would advise against a wall. They NEVER look nice. Theyr'e always cloudy and messy in appearance. The drawings obviously only reach a couple of feet up and you get sick of wiping it down...the dust is inevitable and pens aren't ideal as they work on other surfaces.
I want to create a blackboard area on one wall of the playroom so my children can draw on it. The only problem is we have carpet in that room and I don't want chalk dust ruining it. Has anyone ever used chalk pens? Or anything similar that can be used on a blackboard and wipes of easily, without creating a dusty mess? Are there such pens available? Or am I being naive?!