See it in action on youtube!
(click any pictures for larger image)
I came up with this design over the summer as a way to re-invent the classic marble drop toy. By using a piece of plywood for the back you simplify the construction. Marble track pieces can be nailed or glued very easily to the flat back. If you like, this is a great project to have your child help you build. You can have fun coming up with different marble track layouts. I built mine with two mirror-image tracks, so that you can have races.
(Hearing protection optional... Yes, it makes noise. A handful of steel marbles clattering through the track and striking the bell at the bottom does add up to a bit of a cacophony.)