I had both experiences and found neither valuable. I am in awe of anybody who can learn a foreign language full-stop.

My French teacher fully explained the grammar most of which passed me by since, certainly in my case, one doesn't really rationalise their own language in terms of technicalities.

My German teacher just pitched up on day one and spoke nothing but German. Two years later I was absolutely none the wiser. I could quite honestly have been listening to white noise.

That anybody "picks up" a language is something I am amazed by.