Here are some ideas:
Wobble forward and backward or side to side.
Try with your eyes closed.
Stand on one leg. (carefully!)
Balance a book on your head while wobbling.
Try all of the above (very carefully!)
Play catch with someone while standing on the wobble board.
Time yourself to see how long you can keep your balance without an edge touching the floor.
Common sense woodworking rules apply. Be safe, read and follow the safety guidlines in your power tool manuals, measure twice, cut once, etc…
Materials and tools:
3 feet of 2”x4”
18”x18” piece of 1/2 inch good quality plywood
2 ½” inch wood screws
Circular or table saw
Jigsaw or bandsaw
Sandpaper or beltsander
Grip tape (optional)
Step 2: Mark curved pieces
Step 4: Cut center support and deck
2. Cut an 18"x18" inch piece of 1/2 inch plywood. I'm using Birch plywood, but any nice smooth and strong piece will do. Your local hardware/home/lumber store often carries them in 2'x2' foot sections.
Note: For both of the above steps, use a table saw (preferably) or a circular saw.