So much time in a normal day is "banter" or fire fighting kids misbehaving or distracting each other
Teachers have been saying for years that they can spend more time controlling behaviour than teaching some groups. Was it yesterday or the day before, a teacher was saying they planned different kinds of lessons for the "just after lunch" slot due to lack of concentration etc.
When you look at the syllabus for some subjects, and the text book/study guide etc., it is hard to understand how it can take so much time to teach when you look at the maximum number of teaching hours available. (Yes, I know there are also some subjects with a truly ridiculous amount of content!).
I do wonder whether there is scope to move to a "quality rather than quantity" approach where fewer subjects/topics are taught, but with more emphasis on skills etc rather than learning loads of facts that you just don't need to learn anymore (due to google).
But yes, smaller classes mean less chance for the idiots to dominate and ruin the learning chances of their classmates. I remember a "kid from hell" in our form at secondary school. She was an attention seeking nightmare and constantly being suspended, given detentions, referred to the head, etc. For GCSE, she chose history which I also chose and my heart sank when I saw she was in the same group. There were only 16 of us and I thought it was going to be a nightmare, but no, we had an old-school teacher who quickly got the measure of her and knew just the right amount of attention to keep her engaged without dominating the class. She was still a nightmare in other groups, but quickly calmed down in history. In the end, History was the only GCSE she passed - all down to a combination of a small class size along with an experienced teacher. Doesn't always work though. In our Maths A level class, there were only 12 of us, but the teacher was truly hopeless and we all really struggled. At the end of the first year, she left, and rather than giving us a new teacher, they merged two classes and we ended up with a class of 25 (which is high for A level) but our original class really improved by having a much better teacher, despite the bigger class and less individual attention.
There is more to it than just class numbers, though it's almost inevitable that smaller numbers are better if all other aspects are also good, i.e. a good teacher.