This is very true. The limit of learning in a classroom is the ability of the teacher. The limit of learning in a school is the leadership of the principal. Caliber and esteem of teachers is the one commonality across all high performing systems.

Programs like Teach For America help, but they are tiny compared to the overall size of teachers, and many leave frustrated after a few years.

This situation isn't that different from developing software. If you have great programmers, you can cut them loose with less supervision. If you toss a lot of untrained mediocre bodies at problems, you need to invest a lot more in micromanagement to make sure nothing goes wrong.