These puzzles are all made with a tray & permanent edge. The puzzles are cut deep, so the shapes of the pieces can be seen in the tray below. When playing with puzzles with irregular pieces, the child will look for peices with the right shapes and place them on the tray where they belong. Puzzles are very effective learning tools because children can work at their own pace and they develop the ability to concentrate. Younger children also gain hand movement precision and hand-eye co-ordination.