This is my experience:
* English. Being Swedish, we started with English in 3rd grade, and continued for years. But I suspect that ubiquitous American series and films on Swedish television were way more important than the formal education.
* German. Three years in school, totally wasted. I managed to learn a whole lot of words, and still remember some grammatical rules, but I could not speak German even if my life depended on it.
* French. After university, I decided to take a stab at French. I came up with my own model, that basically consisted in keeping a French novel in my left hand, and a translation in the right.
That worked a lot better than the formal education in German: after a while I could read pretty much anything in French. Unfortunately my method doesn't help at all with speaking and understanding the French. So now I can read Proust, but have trouble ordering a beer in the darned language. I wouldn't recommend that method.
* Spanish. I decided to try another homegrown method with Spanish, basically focusing on listening alone. I listened to Spanish podcasts, radio and TV as much as I could, but not always very actively.
With a little help from some Spanish speaking friends, I am now quite fluent. And it turns out that learning to read Spanish is quite easy, if you already know most of the words by ear. So going from spoken language to written works, but not the other way around (at least not for me).
So, for me, formal language education has indeed largely been a waste of time. But it doesn't have to be. If I could come up with two methods better that the school's, the teachers ought to be able to at least do the same.