The following variation of the famous Tower of Hanoi puzzle was offered to grade 3-6 students at 2ème Championnat de France des Jeux Mathématiques et Logiques held in July 1988. (For more puzzles check the pages of Vincent Lefèvre, France. My thanks go to José Antônio Fabiano Mendes from Brasil for pointing out that site.)
The rules of the puzzle are essentially the same: disks are transfered between pegs one at a time. At no time may a bigger disk be placed on top of a smaller one. The difference is that now for every size there are two disks: one green and one red. Also, there are now two towers of disks of alternating colors. The goal of the puzzle is to make the towers monochrome. The biggest disks at the bottom of the towers are assumed to swap positions.
At the competition, the students were asked to solve the puzzle with 3-disk towers in the minimum number of moves. I would welcome solutions to more general formulations.