Take a look at the ArduinoInfo.Info WIKI here: http://arduino-info.wikispaces.com/Robot+7-wayMultiTrackingSensor
You can make you own equivalent of this sensor array with infrared LEDs and IR Phototransistors, or typical "Reflective Object Sensors" like these: http://goo.gl/lfKlU
But there's a LOT more to this! As the WIKI says: Line following Algorithm?
Now someone just needs to write a function that takes this data and outputs Left and Right Motor speeds from -100 (full reverse), to 0 (stop), to 100 (full forward) and follows a line. Dynamic control based on amount of error would be nice, maybe even PID. See the Video above to get an idea of what is needed.
...but we hope that learning this Mechatronics stuff is why you took the class!
Please make sure you come back and tell us what you did and how it worked out so WE learn something too !
DISCLAIMER: Mentioned stuff from my own shop...