Investigating Arduino project ideas suitable for grade school level.

=== Scratch for Arduino:  http://s4a.cat/

This seems a rather simple extension to scratch which runs a continuously-updated polling loop of the Arduino through the USB/serial interface.  Works ok, but only supports a short list of simple devices.  It would be interesting to see how difficult it is to extend to e.g. Neopixel programmable RGB LEDs.

It installs and runs simply on a Mac running Darwin 14.1.0.  Does not run without major fuss on Ubuntu 14.04 64-bit.  (older Ubuntu ok, 32 bit ok, so they say).

=== Hardware

Analog RGB LEDs seem to run $1 each or more.  

Here are some 5mm ones for $0.79 each:
https://www.superbrightleds.com/cat/through-hole/filter/Color,0,3,103: