All three of mine attended a French immersion school starting in Pre-K. Eldest went through 4th grade, middle through 2nd and youngest through 3rd. I think it was a good experience for all of them. Older two have been IDed as gifted, but not the youngest (haven't looked into that yet - she is only in 4th).
For kids that might be bored by the regular classroom, I think language immersion helps. I think it also makes learning another language easier later on (eldest took German, middle takes Spanish), and it helps with English vocab too (for SATs). Eldest is taking a junior level French course at college now (she is a freshman) and finds it easy - immersion certainly helped.
They had French immersion at a private school. I'm not sure how well the area public immersion programs worked (and I say that in the past tense because I don't think there are any around here anymore). Our district did not have one.
I am curious about your program. If your DS is the only K kid going into the program, how does that work?
