HtDP uses Racket and scales from graduate school to middle school children. Part of the reason they use Racket Scheme is that it is extremely easy to teach the

HtDP uses Racket and scales from graduate school to middle school children. Part of the reason they use Racket Scheme is that it is extremely easy to teach the syntax. As for why it's not used more widely, same reasons Lisp like languages aren't used more often in industry: inertia, fear, worse-is-better syndrome.