For much more information about the theory and practice of natural approaches to language education, see books and articles by Stephen D. Krashen. Many of these articles and books can be downloaded free.
Another good source is the International Journal of Foreign Language Teaching, "a free on-line quarterly journal dedicated to communicating research, articles and helpful information regarding language acquisition to support teachers as they endeavor to create fluent, multilingual students."
For more information about using natural approaches in the K-12 environment, see DiversityLearningK12.
International Center for FOCAL SKILLS provides information about FOCAL SKILLS through its web site.