Where Do We Go From Here? edited by Isaac Asimov (details). A collection of science fiction short stories, each selected with a view toward use in the classroom, and each followed by a series of questions and comments intended to elicit discussion. There is also an appendix with suggested further reading. This book was published in 1971, by Doubleday and Company and has a Library of Congress Catalog Number of 75-142033. Although the book is long out of print, I list it because it can still be found in libraries, because it contains many wonderful stories, and because I have fond memories of reading it myself in the 1970s.

The Golden Duck awards are given yearly to the best science fiction books for children, from picture books to young adult novels.  If you're looking for a good place to start to find good SF for kids, you can't go wrong with their page.  I strongly recommend the 2000 picture book winner - a delightful book called Hush, Little Alien by Daniel Kirk, which has already become one of my son's favorites.

"The Phoenix Trilogy" by M. K. Wren, which consists of The Sword of the Lamb, The Shadow of the Swan and The House of Wolf. (subject matter: history, feudalism; age: high school)  Details

"Africa" series by Michael Resnick, which consists of Paradise, Purgatory, and Inferno (subject matter: history, colonialism; age: middle school and high school).  Details.

Zenna Henderson, The People: No Different Flesh and Pilgrimage: the Book of the People. (age: middle and high school) Details

“Out of Time” series, created by David Brin, consisting of Yanked! by Nancy Kress, Tiger in the Sky by Sheila Finch, and The Game of Worlds by Roger McBride Allen. Details (including description of how a teacher used these books to inspire creative effort among students).

The Mushroom Planet” books by Eleanor Cameron, consisting of The Wonderful Flight to the Mushroom Planet, Stowaway to the Mushroom Planet, Time and Mr. Bass, and one or two more (subject: space travel; age group 8-12 year olds – a good book to read to children). Details

Robert A. Heinlein's juvenile science fiction novels are still well worth reading today.  A complete list of them is here.

Chasing Science by Frederik Pohl is not science fiction, but since a science fiction writer wrote it and since in it Pohl energetically promotes interest in science I have no hesitation in recommending it (details). 

The Borderlands of Science by Charles Sheffield is another book that is not science fiction, but is written by a science fiction author who actively promotes interest in scientifically accurate science fiction, so again I have no hesitation in recommending it (details)