You have 20-30 kids with varying backgrounds, skill levels and learning habits. Some require challenges to figure out things on their own, others explicitly explanations. Some work well in a group, others need individual attention. Some go through a rough patch at home or with friends and are distracted. Some days are hot and you make no progress.

A teacher needs to respond to the dynamics in a large group of non adults, every day, every minute. You can’t plan that out in advance. Sure, experience helps to make the planning easier and to respond to situations you’ve seen before, but still, every day is different, and responding to the challenges in the last lesson requires a plan.

Experienced teachers likely have it down. Or can just use whatever was done in previous years. But you have set standards changed every 10-20 years at least. And maybe new textbook that has things in bit different order. Or there is some topical thing. Lesson planning is really looking at book and items there thinking how much time going over it with current group takes and then considering what items or things are needed in addition to reach those goals for this lesson.

If you had to make a 1/2 hour presentation/workshop, there is some planning involved even if you can just copy paste the slides and training material.

Okay, I get it now. Lesson plans are something that can only be done on the fly and are more about adapting to things outside the control of the teacher e.g. one lesson took longer due to a disruption in the classroom.

I was wondering why the people who set the curriculum couldn't just make a year's worth of lesson plans and email them to each teacher. Thanks for the explainer (to everyone who replied).

Lesson plans are inherently individual to a teacher. So even if a year’s worth of lesson plans was created and shared, and even if I thought they were good, it would still take non-negligible time for me to absorb them and mentally plan how I was going to use them.

That’s the tip of the iceberg in my attempt to explain the complexity of teaching.

> It would be like asking each individual teacher to write a new textbook every year.

This is quite an appropriate way of putting it. It is like that, but there's no real specification as to the quality and length of said text book.

Some teachers create a textbook of stick figure drawings. Others create a textbook of coherent progressive storylines that build on each other using a logical set of figures and well-labelled diagrams that explain the concepts and outcomes that cater to different learning styles.

Now I'm getting out of my depth a bit, as I don't pay a huge amount of attention to the detail of her work, but I believe there is (much?) more opportunity for re-use of materials from one year to the next, thus minimising custom work. But I also believe that she prefers to do it all "custom" for her own (perfectionist? obsessive?) reasons.

It probably depends on the country, but in my country (Germany), the government only defines outlines of what knowledge and skills the students are expected to acquire. The teachers are expected to design a specific curriculum to convey these skills (though obviously constrained by outside factors, most prominently the available set of textbooks).

You’re going to get meme responses about why this is the case from Americans who have never been to countries with centralized education systems, but the only reason that America doesn’t do this is our strong federalism and decentralized, local, education system.

Planning out what the lesson is going to be.