My kids are both in French Immersion at school here in Toronto, in grades 3 and 6. This means that their teachers speak mostly French during the school day, they have to learn French and read and write assignments in French, while the curriculum is the same as that received by their English stream friends. My wife is from Montreal and thought it was important for them to be conversant, if not completely fluent, in French, for the sake of Canadian government jobs or international travel.
I was not a big supporter, but I thought that as long as they were in public school, doing French Immersion would give them an extra challenge to rise to which would stir up their neurons, which could only be good. (Unless they were really bad at it, in which case we would switch.) So far, so good; while not fluent, they certainly know much more French than I did after Grade 12 of the regular stream, which is when I stopped.
But there's more than that. I learned in my Cognitive Science courses that a second language lives in a different part of the brain than a first language. I suppose that because when we first learn a second language we do a lot of mental gymnastics to transpose familiar meanings onto new words. This causes all sorts of metacognitive (translation: thinking about thinking) activity. I also learned that the most important thing you can do to improve your mind is to complexify your thinking, so all in all I was pretty happy about it. Now researchers such as Antonella Sorace of the University of Edinburgh, pictured, are finding that attentional skills in particular are strengthened by speaking more than one language, which they interpret as a boon to multitasking skills. I haven't read the research papers so cannot comment on their conclusions, but it seems to me bilingual people probably also experience benefits to working memory as well as executive functions such as planning and managing.
For more information, visit Antonella's website, Bilingualism Matters, by clicking the link above or the picture here. By the way, clicking the video picture above will take you to her video. Salut, mes amis!