Teachers can teach at any convenient time and location to the student such as a coffee shop, an office, or a library. One-on-one classes are the most efficient because they allow teachers to focus on your precise needs. Explanations are also easier face-to-face.
With a large class size, you can experience the comradery and competition of other students, make friends with people from all over the world. Large group classes allow for a more immersive experience.