Personally I like this better from Roboshop: http://www.robotshop.com/en/dfrobotshop-rover-tracked-robot-basic-kit.html. I'm not sure its right for middle schoolers, might be to sophisticated.
However, most middle school programs use Lego Mindstorms, Paralax Boebot or VeX. Legos are challenging enough for middle schoolers and you can use different software should they prove more advanced. The advantage of the kits is they get something going. Building from scratch, like buying a chasis w/o motors, can be frustrating for noobs.
And 2k is not much. So its good to put the kids in groups and let them play.