There are many forms of karate and some of them have little to do with fighting. If you want to quickly learn to street fight take Kenpo. If you want to learn how to make your body as lethal as possible take a non sport from of Muay Thai.
Note: I took American Kenpo for a few years and liked it, but I don't think it's really the best art for the average 12 year old.
There are plenty of real karate schools, far more fake ones. The test is pretty simple- you ask the instructor if the students fight each other. If no, it is fake. Very hard to get good at something without ever doing it.
Note: I took American Kenpo for a few years and liked it, but I don't think it's really the best art for the average 12 year old.