Language immersion, a technique for teaching and learning a language, has been recognized as early as few decades ago by moderns, but it has been the principal means by which language has been learned by our children since language began. When a child is born, the child becomes part of a family that is part of a community somewhere in the world, in some country or region what is held together, not only be a common history, but also by a common language. The child is inescapably born into a language, immersed in it from the very beginning. Either the child learns to speak and use its native language or that child fails to integrate into its culture. If the child is going to survive, it must integrate, it must learn its language. Such is the goal of language immersion, to immerse the student in a world where only the language to be learned is spoken, where, if the student is to function, the student must learn. How does this work?
Imagine having to go to the bathroom and being required to ask if you may go. You would certainly be motivated to learn how to ask in the language. You're motivated. Those language institutes teaching by immersion will usually supply its customers with a list of such necessary statements and questions. If you go through such training, be sure to ask for such a list. You wouldn't want to have to go and not have the words to ask. But, imagining such a situation, you can see how quickly you might learn a language when knowing it has become the only way you are able to function as a total human being. It's challenging, a bit scary, but it works.
How well does immersion of someone in a language work as a teaching device? About as well as any other technique designed to teach language. Just as in any learning effort, many do, some don't. You might imagine those who don't learn in an immersion class, walking out instead of dropping out. The technique requires twenty-four hour attendance for about five days for basic language training. You sleep there, you eat there, you do everything at the language institute. If you can't learn, or refuse to, you simply walk out and walk up the street to ask in your own language if you can use the bathroom. You just can't come back. Language immersion is demanding, something like the first week of marriage, maybe not as bad.
Most of what you learn in a language immersion training program will be retained if you are sure to follow up that course with a trip to a place that uses the language you just learned. Make that your reward. Hope you don't drown in French.