[NTREEG]

I'm attending a Japanese language school in Tokyo now. Just so you'll have an idea of what it's like...
We use a textbook. We cover 2 - 3 chapters of the text book each week. Each chapter has about 2 or 3 major grammar points that we learn and maybe somewhere around 15 to 30 new vocabulary words. We also learn about 6 new kanji each day.

The intensive language course works well in my opinion. I came to Japan in January and couldn't speak any Japanese outside of basic greetings. I had dinner with some friends last night that I hadn't seen since I first got to Japan and they were pretty amazed that I could hold a basic conversation with them after only 5 months of study. Of course my speaking wasn't anywhere near fluent, but they could understand me and I could understand a fair bit of what they were saying.

I don't know how effective only a month at school would be. You'd pick up some grammar and vocabulary for sure. But a continued effort would be best.