I used to think this way, but some experiences made me realize it's not so cut and dry.

When you have a class size over 20, teachers are forced to be a lot more systematic, which can improve the effectiveness of their teaching. Good teachers make heavy use of social proof. When I tried to teach my kid at home, it was a struggle. But when the kid is around his peers in a classroom, and they are going along with the teacher, he naturally falls in line with no cajoling, etc.

If there were only 5 students, the likelihood he'll just go along with things is much lower.

Yep, that's definitely true. That being said, figuring out which approach to take requires paying attention (which you did), there's no guarantee that any two people (or any one person at two times) will be in the same cohort.