I can't seem to find my copy of the 2009 Scheme Workshop proceedings, but Shriram Krishnamurthi's crew presented some work there that was pretty impressive. They are oriented toward teaching programming to 7-8th graders, before they learn algebra.
They use PLT scheme as the core of their system, but decided to implement it in JS to eliminate difficulties young kids would have installing software, and to simplify sharing of programs for bragging rights (for kids, of course - no adult programmers care about such things).
They use PLT scheme as the core of their system, but decided to implement it in JS to eliminate difficulties young kids would have installing software, and to simplify sharing of programs for bragging rights (for kids, of course - no adult programmers care about such things).