Why? Are they really better than khan academy at doing a lesson plan? Isn’t this like a software engineer complaining they have to write their own database driver in their spare time after work?
In general, it is a good idea to personalize lesson plans based on how well people did or didn’t react to the last one, and khan academy certainly doesn’t do anything like that, nor does it work for everyone.
The entire point of khan academy is that it is individually tailored to the student and can decide what lessons need additional practice vs those that can be skipped. It sounds like you aren’t at all awqre of how khan academy works.
Are you claiming teachers can personalize a lesson plan for each individual student in a class? To a granularity finer than what Khan Academy can do?
Unless you are suggesting a teacher can clone themselves to however big their class size there is, the individualization is not a realistic prospect given that you have to teach a few dozen kids in a 30-45 minute period. And given that current funding levels are having a hard time keeping teacher retention even at these levels, significantly increasing teacher numbers to make real individualization possible is not within the realm of reality.
Also, individual teaching methods don’t work well in certain subjects; as an example, you need a few people to put on a theatrical production, perform ensemble music, or have Socratic discussions.
Teachers aren't paid to personalize lessons though, if you work overtime to do that then you can only blame yourself. Teachers are paid to hold standardized lessons and answer questions help students with problems.
You could argue it would be better if teachers were paid to personalize lectures, but they aren't. Maybe some document somewhere says they should, but in practice nothing will happen to you if you just use standardized lectures so that is what most will do and that is what the expectations of the job is built around.
You say this because you don't know better, but its very common in schools for kids with learning or other disabilities to be in the same classes as other students - called 'mainstreaming' https://en.wikipedia.org/wiki/Mainstreaming_(education)
Teachers are 100% supposed to teach the standardized kids, the kids with disabilities, and the kids who are a little faster than everyone else. It's simply not possible to do with one standardized lecture without individual attention to those with special needs.
It's not some document, its literally a major movement decades old in education.
Lesson plans are not standardized down to the day and order.
Sometimes, a group of students might need to speed up, slow down, or go in a wholly different direction depending on what happened with the previous lesson. There’s a lot of variation between one class of students and another, and teachers are not some kind of omniscient perfect predictor of behavior. And ultimately, you need to cover a whole curriculum.
There is a whole spectrum between teaching centrally dictated lesson plans and individually crafted tutoring, and one of the requirements of teaching is to be able to adjust lesson plans according to reality. We don’t expect software engineers to waterfall every last character in code down to the wire, but teachers are supposed to do this with unpredictable human children?
Why? Are they really better than khan academy at doing a lesson plan? Isn’t this like a software engineer complaining they have to write their own database driver in their spare time after work?