Stack it Up Stacking up rings helps strengthen hand-eye coordination and fine motor skills. Your child can learn how to stack the rings based on the size and color. Classic Stacking Fun Rock-a-Stack is a modern version of a classic toy that has been used by many generations. The Rock-a-Stack has five colorful rings to grasp and stack Bat-at rocker base to help introduce the concept of relative size and stacking. E for Entertainment, E for Education Rock-a-Stack not only develops your baby’s sensory and fine motor skills but also stimulates entertainment.