Once kids reach that pre-puberty/puberty stage, it becomes very difficult for them to learn a language in a formal school setting especially, because of teasing from their peers.

One of my pet peeves. Kids should be taught a second language by being spoken to in that language from a very young age. This can be done as early as kindergarten, for a small portion of the time they are in school, and increasing in the amount of time as they get older and can handle more. I think they should be taught reading and writing in the same way. But most people think I'm a lunatic for thinking this way.