No Korean immersian, "dual language" program in your neighborhood? There's always Korean preschools. Many of them can be found in neighborhoods with high concentration of Koreans, whether it be a CA suburb like Fullerton or a highly populated city like Koreatown, Los Angeles. One of our friends sends their children to one and she said their children's Korean improved dramatically since most of their classmates spoke Korean as the primary language at home. Their lunch menu also consisted of the typical Korean menu for kids, like kook bap (soup and rice)! On the flip side, many of the children are well prepared for kindergarten since most also have a great academic program.
