One of the bigger factors that differentiate between average teachers and great teachers is the ability of great teachers to give a lot of personalized feedback to every student.

Also if other fields of learning like music, sports , computer programming and others, the importance of rapid personalized feedback to learning is very big.

"in virtually every lesson is the provision of an additional teacher who helps those who struggle in a particular subject"

There's a reasonable chance that the most of the advantage of the finish system comes from this method of teaching.