Ah, I work at a lowly school. We don't have teaching assistants. The professors do all the teaching, all the discussing, and all of the grading.
I used to have a pretty poor opinion of the big lecture/small discussion group paradigm, because the big lecture was usually led by some hotshot researcher who had better things to do with his time, and the discussions were led by apathetic grad students. (This was at a very highly-regarded public university)
Eventually, I did a year abroad in the UK, and found their model considerably better. Whereas the department did have an excellent reputation for research, "teaching" was listed first in its mission statement -- and it showed. Specifically, there was never an expectation for undergrads to immediately proceed into a PhD program, which was a huge breath of fresh air, coming from an American Physics program, where one was essentially considered a failure unless they secured a PhD fellowship during his senior year.
Lectures followed a similar format, but were executed far more gracefully. Instead of being led by a hotshot researcher, they were led by a fucking good lecturer -- not necessarily a leader in their field, but an excellent instructor with a passion for teaching. Unsurprisingly, many of them spent a few years teaching before returning to academia (something that would be considered the kiss of death in an American program; publish or perish). Discussion groups also existed, but were smaller, and led by full-fledged faculty members -- sometimes those "hotshot researchers," sometimes fresh new faculty. The groups were small enough that this distinction didn't matter, and there was never any negative backlash from asking the instructor to repeat a particularly confusing portion of a lecture.
In hindsight, I wish I'd stayed to finish out my degree. Upon returning to the US, I immediately regretted it.
