One disadvantage which is common with mass production education is the teaching of students in large groups. In most classes there is usually a small group who would be more comfortable learning at a faster pace, and another small group which would profit from learning at a slower pace. The teacher, however, is constrained by having to try to keep them all moving along together at roughly the same pace in order to get most of them to the required level of attainment by the end of the school year. This results in the faster-learning kids getting bored and the slower-learning kids getting frustrated, although it usually isn’t a problem for the kids with an average learning speed.
Years ago I heard of a private school in another state wherein the children were each given individual packets of instructions, and were allowed to advance through those packets at their own pace instead of being herded as a group. In a system like that, the children could learn more comfortably, but to the best of my knowledge that system is not practiced in elementary schools in areas where I’ve lived.
With homeschooling, I’m able to dedicate individual time to each of my daughters so that each can learn at her own pace. In my opinion, that is one of the key advantages of this form of education.