I understand your concerns, Gabriel, but remember that any amount of overseas experience and study will surely make a difference in your language abilities, but it is what you make of it.  Remember that there will probably be a lot of students there doing the same thing as you, and you may even find other Brazilians or Portuguese speakers.  Are you going to be able to resist the temptation to speak to them in your language, or are you going to fight for total immersion?  They are all there with the best intentions, I am sure, but the temptation can be high when you are homesick or tired and just want to talk to people.  A month is a good length of time, and you can learn a lot and make a lot of progress, but you must be diligent and push yourself. 

A word of advice, before you waste your money.  Do not be over-concerned with the cost of tuition, as much as the quality you are getting.  If the school is cheap but the quality and reviews are low, it is still not worth it.  Also check to see if your government offers any study abroad grants or scholarships.  See if the school you choose, offers some kind of room and board, home-stay, or takes care of complicated and expensive things like student visa etc.  These things are very important to know before you go.  Good Luck

I have spent one year in the US studying at a normal college but as a requirement I had to take one month of English course and I didn't like it. I don't know about this one in California but mine was exactly those language schools in Brazil where the teacher will focus on grammar and follow a book during the class and make each student participate in one exercise. The good thing was that in my classroom everybody was from a different country. What worries me in your post is that it's a school for Brazilians. That sounds depressing to me to leave Brazil in order to spend a lot of hours at a school with other Brazilians! No good at all! And remember to engage in cultural activities while you are in the US. Make friends, go out, participate in meetings that you can find at meetup.com so you can have other people around you!  

Here’s my two cents’ worth: Experience abroad is great, but as the others have mentioned, it all depends on what you make of it. As far as the tuition, since labor costs are relatively high in the US, where fast food employees make around $10.00 an hour (or more in major cities), it’s not possible for any school to offer a good student teacher ratio. I’m not saying that oversized classes with unknown instructors and methodology are necessarily worthless, but I am saying that you could do much better finding some good teachers here on italki and taking private classes on line. The great thing about italki is that each teacher’s profile gives you a lot of information to make an intelligent decision on who can help you the most, and there’s no upfront cost anyway. After you’ve improved your English here with professional teachers, tutors and language exchange partners, you can go to the US (or wherever you'd like) and do whatever you want, and you’ll have a lot more time for fun and real education (meeting locals, exploring, understanding the culture...), since you won’t have to waste time commuting to a boring class every day.

Gabriel! I guess I misunderstood your post, first I thought it'd be a school for Brazilians, that scared me hehe. Sorry! A school in SF would definitely have lots of different nationalities! So, go for it!