Strengths of Individuals Build the Class
Some students are great at reading notes

Some show their strengths in feeling or playing rhythm. Others see patterns everywhere and get excited when they search for new ones. Even a student with personal discipline in practicing lifts those around them.
A whole class can learn from the strengths of others and even from weaknesses too. Where one will shine in playing rhythm games, another will stand out in sight reading. It is awesome to see class members cheering for each other. Win Win.
This is missing in private lessons
The strengths of individuals can help build a much better learning experience for all of the students in a class. Typical private lessons cannot provide this benefit. When I showed up to my own private lessons, having been required to practice for 60 minutes a day at home, I had zero idea that it was a great amount of practice time. But I wasted a lot of that hour each day. It would definitely have motivated me to focus better and work to accomplish assignments more diligently if I knew that my practice was above normal.

Instead, I never measured my own progress. Not once.
The converse of this is true as well. When a student comes to class having played the minimum amount that week, they see others who put in more effort and that effort shows with their progress everyone can see and hear.
Private lessons are typically just a connection between a teacher and student
Motivation for learning is extended to include the class where the teacher is seen as a coach rather than a judge. Think of soccer practice where the coach lines all the players up to practice a shot on goal. The players all enjoy shooting and watching their kicks and how their teammates are scoring. Soccer kids will work better to practice their kicks when they are doing it in soccer practice. The same goes for piano practice when we line up to play for each other each week.
Rhythm skills that bring the whole class up to par

I was a terrible counter when I learned piano. Notes were my strength, not rhythm. Each week when my teacher had to correct my timing it was torture. Here’s where having a student who thrives with rhythm brings energy to the whole class.
I use all kinds of modalities in class for teaching rhythm. The sticks are Eli’s favorites. Every week, as he walks in the door, he asks if we’re going to be using the sticks today. Sometimes he gets the others to plead for the rhythm sticks as well. How can a music teacher not be swayed to bring out the tools of learning rhythm? That entire class will score head and shoulders above the rest because of Eli’s love for counting and playing.