My kids attended/attend a French immersion program at a private school. All started in Pre-K, eldest went through 4th grade, middle kid through 2nd grade, and youngest is currently in 3rd.
Like CCN, we have found a lot a bright kids with education focused parents. However, that may be in part due to our location (affluent, educated area, many 4-year colleges nearby). My older two are now in HS. Eldest is fluent and took the French AP test after 10th grade. My middle kid, who only went through 2nd, is not fluent but finds HS French and Spanish to be easy.
I recall hearing about a few public school immersion programs around here back when my older two were young, but I don't think they are still in operation. I don't know if those programs turned out fluent kids. If it is done right, it can be a great experience.
