If you already know the basics of English, I recommend you go with an internship to study English instead of language schools.
There are few Americans in language schools, the only ones being teachers and clerks. The majority are non-Native English speakers. The reason I chose an internship to study English is because I thought that I couldn’t talk a lot with American people in the US. I found this to be true.
Another reason is that you don’t have to speak English a lot in classed; what you need to do is to concentrate on listening to the teacher’s lecture. Of course, it’s necessary things to read and listen to English, but only these passive studies aren’t enough to learn English. You also have to speak and write a lot English.
You can’t learn natural English only through language schools. I speak with a lot of American people daily, listening to their daily conversations. This kind of natural English sometimes includes dirty words which aren’t taught in school. If I only studied in school, it would be difficult to learn these kind of dirty, but natural English.
On the one hand, a school is safe place for you. The staff usually don’t get angry with you, and blame you for something, so you don’t need to be serious. On the other hand, if you choose an internship, you have to talk with people who aren’t nice to you. Now I have to talk with people who are in a bad mood; it’s completely different from schools.