Goethe's test center is Zürcher Hochschule Winterthur. I just completed a ZMP prep course that lasted over three months and took the test there. I would say a few things: experience is dependent upon the instructor, my class had a strange (and not always comfortable or intelligent) mix of people, and classes can be up to 18 in size. However, the curriculum was great. One of my two instructors was clearly extremely experienced, knew English / Spanish / French at the very least, and did an amazing job conveying the material. One person in the class attended both ZHW and Benedicte -- he said ZHW was far, far better and moved much faster.

However, they have a limited time frame for sign ups, as they do not operate like normal language schools. You might want to check out their website, but I have the feeling that it just ended. I decided against returning there because I want to find work and want something that has smaller class sizes and encourages much more independent work. We would often sit in the classroom and do exercises alone, then go over them. It was a massive waste of time. It would have been much more intelligent if they had divided us into smaller sessions and made us do the work at home. But, then again, some of the people there were not that bright. As it is a Hochschule (state college), there are a number of refugees there subsidized entirely by Zürich, and they most definitely drag down the pace and reduce one's ability to learn.

I personally find it essential to take a German course to at least the B2 level before trying to teach yourself. It is not easy for English speakers to learn dativ, akkusativ or genativ -- or at least it was not for me. There are a lot of extremely strict rules, all of which need to be memorized and taught systematically, which is what I loved about ZHW. I had German prior to my arrival in Switzerland back at college in the States, during which time I felt as if I had learnt practically nothing. As grammar is not typically taught systemically in the States, it is (practically) impossible to learn German without being forced to go through this process while learning it. The rules are everything.

However, I have found it essential to a.) watch TV regularly and b.) read a newspaper regularly. I really enjoy bringing my laptop in front of the TV and then typing words that I do not know into an online dictionary (Leo). Also, by reading a newspaper daily, you learn to recognize more complex sentence structure, pick up on vocabulary that would not normally appear on television and learn more about Switzerland. I read the NZZ because I want both in-depth international and Swiss news, but most say that is too difficult to start with. My two cents.