Good point about the student losing motivation in the private lessons, and fact is, I find that I also lose motivation. A small group is more dynamic. Think of making lunch with only peanut butter as a main ingredient. You could go through several lessons making them interesting as you go, but it begins to take more and more work.
However, the same lessons begin to take less and less effort in groups as the groups start to "take-over" the learning process. This is true in a classroom as well. If you set them into a rountine that teaches them how to eventually "take-over" the class, they'll settle into the routine earlier into the lesson and the effort on my part as a teacher become more and more effortless.
For example: Speaking and listening requires a speaker. In a private lesson the only person doing the speaking is the one student. This gets boring quick because their mistakes are usually the same, and both of you know what to expect. Loss of motivation means higher turnover. In a group, each person brings a different personality, and the chemistry and unexpected surprise of what the next person will say makes the same lesson more interesting.
By starting a pattern of teaching that lets the students know your expectations, those same students gain confidence in their own abilities and the speeches become more free-flowing talks than the stilted memorized versions they were giving at the beginning. A pattern I've developed that works well was based on the debate model.
- Introduction and presentation of topic.
- Questions for understanding and discussion.
- Answers for clarification and opinions for further discussion.
- More opinions.
The first few times I introduce the topic, let a student give a speech, then I allow them to ask about anything they didn't understand and then I ask questions to elicit opinions. I slowly hand over the parts I do to the students. I begin to expect them to introduce the topic after I've taught them what I expect in an introduction. I teach them what "questions for understanding" are, and then I expect them to come up with their own.
As the class begins to "take-over" the learning process, you can relax more. Crazy thing is, the more they can do on their own, the better teacher they think you are.