OK... on to the tutorial.
Step 1: Gather supplies
self laminating sheets
white board marker
At the bottom of this post you will find two downloadable files. One is a psd file that you can download and use to customize the chart I have made if you have Photoshop. The other file is a plain pdf file of just the blocks, so you can print it out and write your own stuff on it. You can also draw up your own on your computer or by hand. Or perhaps get the kids to help. It's your choice. Either way, create your chart and print.
Use your self laminating sheets to laminate your charts. If you don't have sheets or can't buy them, there are places that you can get them laminated for little money.
Glue on four magnets on the back... and ta da! Your done.