How has Arduino been used in the classroom? I remember seeing Primo, this robot that is based on Arduino and serves to teach kids to program. My interest in the platform comes from there, but it is always nice to learn about other cool applications.

What other applications are there that utilise Arduino for K-12 education?
I've used Sparki from Arcbotics as a robotics platform. It's uses Arduino Sketch to program and a modified Arduino IDE.

Sensors for line following , edge detection, distance and light level sensing are built in. Also the creators are focused on education so the material and projects are teaching oriented.

The Community seems pretty active and engaged too so the material should build over time.