That's not particularly demanding requirement. The class began with a single lecture about how Scheme worked and after that Hal and Gerry assumed you knew all the language you needed to and dove in.

When the course was introduced (early 80s), most incoming MIT freshman had not programmed a computer (!), including those who planned to do course 6 (EE or CS -- 6.001 was a requirement for either degree).

First-class functions, lambdas, closures, lexical scoping, etc. Abelson wrote, for instance:

"6.001 differs from typical introductory computer science subjects in using Scheme (a block-structured dialect of Lisp) rather than Pascal as its programming vehicle. The subject's developers feel strongly that Pascal is hopelessly constraining, and that important ideas (such as functional programming and object-oriented programming) can be addressed within Pascal only awkwardly, if at all."

no, i'm referring to the fact that this book isn't language agnostic (i.e., you wouldn't want to use anything other than scheme/lisp).