What a fascinating and fantastic book! Madeleine L'Engle calls it "science fantasy." I found it amazing. Enchantress from the Stars by Sylvia Louise Engdahl was republished in 2001 by Walker Publishing. Formerly, a 1970 Newbery honor book, I'm wondering how I could have missed it the first time around. Space travel, colonization, magic, dragons, mix with a benevolent race overseeing less advanced worlds. The book was compellingly told through three viewpoint characters and very difficult to put down. It's one I'll have to purchase for myself.
Read about Sylvia's other books at http://www.sylviaengdahl.com/