> One thing I dislike about language group classes is that you learn with other non-native speakers (and, in general, with the same experiences that you have).
> In other words, you learn and re-enforce each others' common mistakes, misconceptions, mistranslated idioms, and ambiguities in the language that native speakers find instantly jarring. This worsens if the teacher is non-native: I wouldn't place much value in such a class.
I absolutely second this as someone who has taken 3/5 semesters of Chinese. Some classmate's pronounciation is so objectively wrong that I have to pay attention for when they're called on just to mute my volume output. Obviously I can't do this in-person.
I've taken one-on-one courses in another language and it's (believable I suppose) how much faster I've progressed.
Another fault is that some classes are structured so that nobody fails or falls behind (whether they're night classes, at a school, or in a corporate environment). The fault with that is that many other subjects simply don't care if 1/3 of the class fails, but language group classes tend to go at the speed of the lowest individuals.