Nothing wrong with classrooms as long as they provide activities that are similar to the experiences one has in an exchange program abroad, for instance. What matters is not the place, but the environment. An environment of the target language and culture can be created anywhere with native speakers.

The idea of "teaching a language", in the traditional sense, that a teacher conveys his knowledge about the language, explaining grammar rules, prescribing translations or parroting sentences and performing oral drills, will provide only a marginal benefit, merely in a complementary role.

You may find useful our pages about Native vs. Non-Native Teachers at http://www.sk.com.br/sk-nativo.html and also our page about Acquisition vs. Learning at http://www.sk.com.br/sk-laxll.html