This is not the Dai Vernon cups and balls illusion, which is what you'll get if you Google Cups and Balls. It is the illusion I mentioned in Beyond Disbelief, and the version my son learned first (so for me, somehow, it is more "authentic" than the more popular version.) The Dai Vernon version is harder for young magicians, because it requires you to repeat very smooth palming and placing of the balls, but if you watch it often enough you can probably see what is going on.
Set-up: table or other flat surface, 3 cups (any size large enough to hold 3 balls), 4 balls (sponge or yarn, rubber will bounce and not work). Stack the cups up (A-B-C), placing one ball in cup B so it won't show. Place the 3 remaining balls in a row parallel to your body (left - center - right) in front of where you will place the cups.
Start of the Effect: Show the stack of cups, inside and out (nothing here). Put cup A on your left, B (the one with the ball) in the middle, and C on your right. Be careful that you move smoothly but quick enough that the ball does not drop out of the B cup (this is why bigger cups make the trick easier). Now place the first ball on the top of the B cup. Stack A and C on top of B, and say whatever patter you like about moving the ball through the cup. Tap the stack, then pull it off as a unit, revealing the ball on the table.
Middle Part of the Effect: Do not move the ball on the table. Instead, take the cup stack and reset the three cups from left to right just like you did before. That means the first cup (B) will go on your left, the second cup (A, with the second ball) will go in the middle, and the third cup (C) will go on your right. Again, move smoothly to get the ball to drop without being seen. Put a ball on the A cup in the middle, stack C then B on top, patter, tap, reveal 2 balls under A.
Final Part of the Effect: Reset the cups again - A on the left, C (with the ball in it) in the middle, B on the right. Repeat ball, stack, patter, tap, reveal 3 balls under C.
Not a particularly hard idea, but a solid trick for people just starting. The key is being smooth with the cups, and that takes practice. There are a ton of advanced variants on it, the most popular of which is the Dai Vernon version. In that version, the balls are all placed on top of the cups at the start of the trick, and then through a series of drops and palms placed first under the three cups and then all three in the middle. If you can do it smoothly this can look amazing - Penn & Teller have a great version. Still, for beginners I think this version is superior.
