Step 1: Gather materials & tools
First you have to choose what dimensions you would like for your Jacob's Ladder. There is a great deal of flexibility here: you can make a wide and very long Jacob's Ladder, or a thin and/or short one. The size and length of the board and ribbon needed vary accordingly. However, for a project that, say, a 9-year-old can do with a parent, the following specifications may offer the best combination of workability and aesthetic appeal. A thinner board (say, 'lattice board') than what we have used is possible but makes hammering the brads in particularly hard for a child (or a clumsy adult like me).
1) 1/2 x 2 inch wood board, length of 24 inches or more
(I found this at Lowe's grouped under 'Molding,' not in the raw lumber aisle. It is labeled as 'S4S', whatever that is. So-called 'lattice board' is, I think, 1/4 inch thick -- too thin for easy use.)
2) small nails/brads
(They have to be small enough not to pose a splitting problem going down the thinnest dimension of the board. I found that 3/4" x 17 'wire nails' did nicely. You do want the nail to have a head, not just a straight brad, and the head should be flat to offer a flush profile.)
3) 9 feet or so of 3/8"-wide cloth/polyester ribbon
(You can get this at a craft store, e.g., Michael's. Go wild with the colors -- you can use up to 3 different colors in one Jacob's Ladder.)
1) small hammer
2) ruler, straight-edge, and pencil
3) hacksaw or power-saw
5) sandpaper (perhaps coarse and fine)
Step 2: Prepare the blocks
Saw each block off. If you are a hack like me, you won't get these to be perfectly equal lengths. This project is pretty tolerant of such errors, but do your best to make them equal lengths and cut at 90 degrees.
Your blocks will no doubt have shaggy ends from the sawing. Use sandpaper and smooth the ends off. Do not round the ends -- you want to have nice square corners and flat block ends, though some slippage here is no big deal.
Step 3: Prepare the ribbons
Step 4: Nail the ribbons to the first block
The second picture below show what you want your first block to end up like: two ribbons attached to one edge at top and bottom; the third ribbon attached to the *other* edge in the middle. I am going to call the pair of ribbons at top and bottom 'blue,' since that is what they are in the picture, whereas I'll call the middle one 'red.'
To start, hammer the two blue ribbons into one edge of the block as shown in the next picture. Make sure all your nails/brads henceforth are flush with the edges -- but keep in mind that overkill can break your block. Now you see why we are working with 1/2" board. It would be too difficult to keep the nails from going diagonally through the side of the block if we used much thinner board.
Flip the board to the other edge, as shown in the third picture below, and hammer the red ribbon into the middle of the edge, so that it folds across the same top of the block that the two blue ribbons do.
Step 5: Add the second block
Turn the blocks on one edge and hammer the blue ribbons in on the edge you are facing. Then flip to the other edge and hammer in the red ribbon.
BUT WAIT! VERY IMPORTANT You, like me, may have the impulse to overtighten bolts, ribbons, etc. Do not indulge that impulse here. Before you hammer in the second block's ribbons, make sure there is enough loosey-goosey space. The slack in the second picture below is a good cue. You can scoot the ribbon with your nail to make a bit of slack before you hammer it in. A 1/4" would be enough, I think, though I just went by feel. If there is not enough slack, the whole creation will stick without flipping properly. Try to make the ribbons have an equal amount of slack, though.