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Also on these boards
Bottle marble run. This would work on the water wall I have posted. Just use nuts and flat end bolts and screw onto a peg board from home depot. You can cut off the mouth of the bottles to make a larger opening and use golf balls or other balls. Cheap and easy--but so much fun!
Marble Races with a cheap pool noodle (keep kids occupied for hours.)
Using a pool noodle to create a racetrack for marbles. Would be great for science when working on speed or friction...