I have one bulletin board in my classroom (and one just outside of it). I use this board for the projects that all grades are working on. I find that the younger kids love looking forward to the projects the older kids are working on, and the older kids recall skills and terms that they learned previously when they see the younger kids working on them. This year I added my "Learning Tagets" near each project. Although not all of the kids can read them, it will also remind me to touch on those concepts during our discussions and assess learning on those items.
Learning Targets are written using "I Can" statements, which I find really easy to write, and the kids find easy to evaluate.
Here is the outside of my classroom door. My room was the stage when the school was a high school, so it has a frosted plexiglass window that I covered with the large poster.