I'm definitely not thinking of SICP, but now that I look at the table of contents of _The Little Schemer_ I must have been thinking of another book. It had an innocuous title but very tricky and subtle contents. It wasn't very long. And it wasn't _Simply Scheme_ either.
Okay. If it helps, the formatting for _The Little Schemer_ is very distinctive: a lot of short question-and-response pairs, with (perhaps overly) cutesy drawings of elephants. _The Seasoned Schemer_ is harder, but it's the sequel.
If you like the format, _The Little MLer_ is one of the best intros I've seen to ML-style type systems.
I don't recall _The Little Schemer_ being any kind of gentle introduction.