Free online tutorials that provide a quick-start guide to Scheme.
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"Teach Yourself Scheme in Fixnum Days" is an entirely free resource.
Pro Straight-forward introduction to Scheme
Rather than using Scheme as a way to teach various areas of computer science, "Teach yourself Scheme in Fixnum Days" purely teaches the Scheme language.
"Teach Yourself Scheme in Fixnum Days" is noted as being outdated in some areas (for example, its introduction to macros using an unhygienic macro system).