I found this great post by Teach-A-Roo about a formative assessment plan and I had to adapt it for my own classroom. If you click here you can see how she uses this board in her classroom and it has a link to her free sign.
I decided to make my squares in the shape of tickets. Here is my board ready to be laminated:
The idea is students answer a question on a sticky note and put it on their student number. I plan to ask a question each day and have them post as part of their end of the day routine. I can quickly see who gets it and who doesn't.