I had the option of "teaching" every year in college, lab courses. The freshmen were the best, they were most inquisitive and mostly cheerful, eager to learn. The seniors were pretty much going to med school, they were really smart, mostly, but beaten down quite a bit, they put their heads down and did whatever was needed.
The sophs and juniors were the worst, they were a mix of kids going to med school and kids with little shot at it, they were always asking "Is this going to be on the test?" and "Why do I need to learn this?". They were often whiners.
I can't remember anything about 8th grade. That was high school for us, they didn't have junior highs.