The BYO-bot is a great introduction to the world of robots. They have also been used as an introduction to transistor electronics, demonstrating feedback, closed-loop control, etc. BYO-bot kits have been assembled sucessfully by children in grade three and above, and even younger children (with a little parental help) have been able to put them together.
The robot can be reprogrammed in a matter of seconds. The robot can be programmed to follow a line. All the major parts of a robot (power, motors, sensors, computer, structure, etc) are plain to see and easy to work with.