Malcolm Gladwell, John Hattie and Warren Purdy all have something in common- the belief that small class sizes have no appreciable affect on student learning.
I'm currently reading Gladwell's David & Goliath (Underdogs, misfits and the art of battling giants) wherein he expands on the class size debate.
Interestingly, he makes the claim, based on American research, that a really really small class is as bad as a really really big class. About 18 is the ideal number to get it right re atmosphere (vibe!), discussion, rapport, and recycled teacher jokes.
John Hattie broadly agrees. His effect size meta-analysis indicated that class size has no affect on student learning.
Curious then why so many people (yes - for that read PR people and parents) think a small teaching class is beneficial. Conventional wisdom is at the heart of that false perception I believe.
A class of three might sound like an ideal but it's my idea of a nightmare.