MaThketBaLL!
"Mathketball" is a learn-as-you-play sort of toy. Modeled after the classic basketball, with a few modifications, Mathketball helps to teach children about elastic collisions (the ball with the ground) and gravity. Unlike the basketball we know and love, Mathketball has colored lights where a basketball would have black lines. These lights use the weight of the ball being dribbled to close a circuit and light up (much like the children's tennis shoes, L.A. Lights).
Additionally, there is a math function (hence Mathketball). The ball itself will ask simple addition and subtraction problems. To answer, a child will bounce the ball. For instance, asked a question of "what is 1 plus 3?," a child would bounce the ball four times. If the answer is correct, all the colored lights light up. An incorrect answer triggers just red lights and a prompt to try again. For younger children, the math function can be turned off, and Mathketball becomes just a ball again.
Mathketball would cost approximately twice as much as a regular basketball, simply because the cost of making it would be greater. Like a basketball, however, the rubber used in construction would be very durable, and though the lights may burn out and the math function may be outgrown, the ball itself would last for a very long time, depending on the amount of use it gets. The ball is large and no parts can be swallowed, but will be rather heavy and so is not appropriate for the smallest of children.