One thing with immersion programs is that they generally don't have many entrance points. I'm guessing in your case you'll have to decide in grade one and likely wouldn't be able to opt in at any other point. With that in mind I'd be more likely to at least start it and see. You can always go back to English at any point if it isn't working out. He might be a bit behind after a couple years of full immersion but for most gifted kids that can quickly be caught up if needed.
I was also thinking about it a bit more and even if we had had a
choice we likely would have started in immersion. I grew up in a neighborhood where many kids spoke at least 2 languages and I now work in a very multicultural environment. I never really thought anything of it until I was backpacking around Europe with a bunch of people from various countries, many of whom were having a hard time adjusting to being surrounded by foreign languages. For me it wasn't a big shock, it was just like any day growing up (although I admit I find it more challenging being in countries that are based on different alphabets so I can definitely empathize).
How much of a solution it will ultimately be will depend on the teacher and the make up of the other 24 kids as well as your child's excitement about learning the language. I know for my daughter it is working really well. Learning French is something that we can't do as well at home as they can do at school and it is giving her something special to learn at school.
