>>1706713Both.
Classes help with speaking, because you have to speak in class. Other than that classes are sort of shit.
You'd probably make more progress studying by yourself, to be honest, than classes. That is if you're one of those guys that's self-motivated. By that I mean you don't need a test or an essay or even the maintenance of your GPA to keep yourself motivated to study Japanese.
Don't expect to "know" Japanese if you get a good grade on a test though. Not to sound like a condescending cock, but I'm pretty sure I have one of the highest on record subject GPAs for Japanese at my university but at the time my "practical" Japanese was a mess.
In short: classes are cool because they make you speak, but they're not so cool because they (from my experience) don't actually teach you much practical Japanese. You'd be surprised at the number of 4th year Japanese students who can't even begin to read authentic literature, when it is entirely possible to be able to engage with real Japanese after 4 years of even moderate studying.