Why do you think we don't? Different teachers, institutions, and educators have used differing curricula and systems and styles education for all of history. In modern times in civilized countries (and states) they are even required to update their knowledge over time and interact with other educators and experts to improve their techniques, knowledge, and systems. Large government education bodies regularly try to put a scientific spin on the process but it's often clear they aren't being rigorous or honest with themselves.

If your local educators are not required to participate in this system of continuing education and improving techniques, that's a local government decision and you should seek to fix that.

Fixing it is often hard in the states because there is a not insignificant amount of Americans that see schools as undermining their authority, see education as a useless and undesirable endeavor, often as a "radicalizing" and "socialist" influence and institution, and so they fight back against any improvement of schooling. There are states in the union that allow pretty much anyone, with no qualifications or certifications, to become "educators", and other states in the union that require a masters degree and 12 credits of class work every few years to continue to be an educator. Outcomes often imply a correlation between those requirements and the result, and yet the states with much lower bars of entry do not increase them. Education in the states is a politics issue, for some stupid reason. There are people who believe for whatever reason that middle schoolers are being taught "Critical Race Theory", as if that isn't a college level course that the vast majority of humanities majors don't even experience.

Start up idea