Scheme is a mature Lisp language which was also widely used as a teaching language e.g. at MIT, where it was the basis for the famous
Structure and Interpretation of Computer Programs course. The course is available as a free online book at the website, and videos of the lectures are also available. SICP teaches the fundamentals of computer science using Scheme, which is fascinating - but challenging - stuff. If you want a more accessible introduction to Scheme, the book
The Little Schemer takes an interesting and surprisingly effective Q&A approach to teaching the basics of Scheme.
If you expect to be doing a lot of coding in Scheme, you'll need to
learn about functional programming as well as Scheme/Lisp. Depending on your background, you might find Neal Ford's
Functional Thinking articles on IBM DeveloperWorks helpful.