The only caution I would have about the immersion program is what type of kids would be in the program. Would the program be mainly English speaking children? If there would be a mix of English speaking and Spanish speaking children you would have to be aware that many new immigrant Spanish speaking children tend to track severly behind English speaking children. As a result, the class may function at an extremely slow pace.
I haven't really seen a lot a research regarding immersion programs for the long term.
As long as the class will function at a good pace, doing the language immersion might be good. I am not sure I would hold my child back academically for the language though. Especially Spanish as it is relatively easy for English speaking children to become fluent in Spanish. My son (16 months) recieves Spanish language instruction twice a week for one hour and is already pretty good. If it were an immersion program for Mandarin, German, French, or another language a little less familiar to English speaking kids I would definitely consider it though.
