Private lessons are the best kind for people who aim at learning at their own pace. This is because-
1. The lesson speed can be adjusted to your own learning speed.
The lesson can speed up where you feel comfortably easy, but slow down where you are finding it harder to learn. In a group lesson, of five students for example, there are as many level differences as the number of students. Some students are quick at learning some things but others are not. There are also some differences in motivation: some people study the language as a hobby, but others have a particular goal.
2. You can ask as many questions as you wish.
This means you can always feel your understanding of grammar/functions is clear and you feel ready to go to the next stage. In a group lesson, you may sometimes worry about asking questions as you might feel that might slow the progress of the group
3. You can re-schedule your lessons at your convenience.
When you have something important on a day when you are supposed to have a lesson, you can re-schedule this on a different day. Thus you will not waste your lesson funds. In a group lesson, you cannot do this as all the lesson dates/times are already fixed.
4. Should you become too busy to take face-to-face lessons you can switch to equally effective Skype lessons.
Shipra, who has been studying with me for a couple of years, is sometimes very busy so has her Japanese lessons in both formats – face-to-face lessons when she is in London, but Skype lessons when she is abroad. In a group lesson, obviously you have to miss the class when you cannot physically attend the class. See Skype
5. Having said all of these, there are good aspects to group lessons. For example, you can meet other people and have conversations with them. You can hear different pronounciations.