Someone mentioned Podkayne of Mars above in this thread. My older D was kind of traumatized by that book because Podkayne (main character) does not survive. I had forgotten this (loved that book as a teen), so just something to be aware of.

Another good book is "Lotus Caves" by John Christopher. I think it may be out of print, but it is so easy to find used copies of books in great shape on the internet that I thought I would mention it.

(By the way, does anyone else find that they can't see any dates for posts on threads out here? I have NO idea how old the original thread is...).