I went here: http://www.derzhavin.com/en/

It is 4 hours per day, 5 days a week. All classes are "Russian only" no other language is to be spoken in the building. It is not as expensive as a lot of schools and you can go there as little or long as you want or can afford. I would say it helps but it takes many months or years to become fluent.

You can also just forget the schools if you want and simply hire a Russian private tutor 2 hours a day for cheaper than the schools will offer. I did this also, and prefer the private tutor method because i got far more experience in actually speaking Russian while in class with a private tutor plus it is cheaper and lessons can be arranged when around your schedule! here is the website for that: http://easyrussian.ru/company.html

It is just a couple of women who coordinate times to meet you for lessons in st Petersburg cafes and bistros. You can negotiate your own prices. Tell them i said "Hi"!