How to Master a Language for Life
When you realize that the main reason to take language classes is to practice speaking and receive corrective feedback, it becomes a matter of simple arithmetic to understand that smaller class size equates with more efficient learning.
Let’s consider a well-managed one-hour conversation class. Perhaps the teacher provides some introductory and concluding remarks to motivate and guide the students, which take up, all told, 10 minutes of class time. The remaining 50 minutes are used exclusively for students to speak and for the teacher to provide corrections and other useful feedback.
If there are 2 students in the class—assuming they split time equally—each student gets 25 minutes of invaluable, intensive practice. If there were 5 students in the same class, each would get on average 10 minutes of practice—60% less, but still a reasonable amount, especially if other factors, such as cost and socializing, make the overall experience worthwhile. But if there were 15 students in the class, I would say, “Don’t waste your time”, because each student gets just over 3 minutes of practice. By contrast, in a 1-on-1 class, the student would have the entire 50 minutes of intensive practice and make fast progress.
It's that simple.
Other arguments either are based on false premises, are merely subjective, or are otherwise unrelated to efficient language acquisition.
Traditionally, many language courses, like education more broadly, were based on the model of a teacher-specialist lecturing and students passively listening and taking notes. In this approach, class size matters little, and it is actually economical to have very large classes.
However, this model never made sense for language acquisition, and it is increasingly obsolete for education in general.
Unlike an academic subject, such as history or linguistics, which you can mostly learn simply by listening to a great professor discoursing on it, languages must be learned through engaged practice. Furthermore, with the advent of YouTube and other means of mass communication, you can watch and listen to the best professors and specialists giving polished lectures any time, at your convenience, and often for free—regardless of the subject. Thus, the traditional university-lecture model no longer makes any sense.
In language acquisition, the main reason to listen to others speak is to train your ear; but it is vastly more enjoyable—and consequently more efficient, since your attention is fully engaged—to watch movies or whatever type of authentic audiovisual content you are most interested in than to listen to a professor go on and on in front of a lecture hall. Even if you are seeking motivation, grammar, or “tips and tricks” in the language, you are better off getting them through books or prerecorded videos than in large group classes.
Some people reason that it is useful to hear other students’ mistakes getting corrected. This is inaccurate. Yes, you might learn something, but at best it is an extremely inefficient way to improve. At worst, you will also pick up other foreigners’ imprecise modes of expression, and who wants that?
Another argument given for eschewing individual or very small group classes is the social enjoyment of lively conversation. This preference is completely valid, for the sake of enjoyment or making friends, but it has nothing to do with efficient language learning.
Perhaps the most important argument in favor of larger class sizes is the cost reduction. If associated with the social-enjoyment motivation, having classes with a handful of other students can in fact make a lot of sense. You can get low-cost, high-quality instruction, make friends, and progress consistently. There is a limit to this rationale, however.
I would much rather pay, say, $45 for a one-hour private class than $3 for the same class with 14 other students. While in either case I may be paying the same amount (about $1) per minute of intensive practice—i.e., my speaking and getting feedback—I also must factor in the cost of my own time. In fact, I wouldn’t take regular classes with 14 other students even if they were free, simply because my time is far too valuable to spend (as in the above example) 42 minutes listening to other students’ mistakes just to get 3 minutes of intensive practice. My language acquisition would benefit far more by spending that hour reading a book or watching a series on Netflix.
So, what is the ideal class size? If you want to maximize your time, it is just 1 student—i.e., you and the teacher. If you enjoy the social interaction of group classes, then a class size of between two and six students is reasonable: just remember that you will need to proportionally increase your class hours to get the same amount of all-important intensive practice, and thus make the same amount of progress.
Lastly, don’t forget that most of your acquisition can occur outside of classes, since you may practice reading, listening, writing, and review activities on your own time. Classes are required to improve your speaking and to receive corrective feedback.
 Of course, in reality, more talkative students obtain more practice, while more introverted or very polite students get much less.
 The theory of deliberate practice helps explain the fundamental importance of speaking while receiving corrections and feedback from trained, professional, and preferably native-speaking teachers.
See other blog posts