These little puzzles lend themselves delightfully to the independent contract situation.
Puzzles come in six colors with the colors indicating increasing difficulty.
Yellow is the simplest puzzle proceeding up to purple as the most difficult. The initial goal of attacking such a puzzle is to put the pieces together in such a way that they form a three dimensional cube. Pieces must fit smoothly and tightly together with no corners left partially closed. Thus students can self correct their choices as they try to assemble the puzzles. When a student has mastered each of the colors by forming a cube, the next step is to combine two cubes into a rectangle with additional formations possible for three, four, five, and six cubes respectively.