Because even I don't want to work 9-5.

(Also, when are teachers supposed to do things like grade work, or kids to have extracurricular activities, 9-5 is draining, add in music or sports and there's nothing left)

There are compelling reasons send them 9-5

There are also compelling reasons not to

1. Teachers spend a non-trivial amount of time post class working on previous assignments, future assignments, setting up tests coordinating with other teachers and staff. If they start all this at 5, they're stuck at the office until very late.

2. Busses/kids on the road before rush hour

3. Extra-curricular activities are better off earlier than later, don't want clubs running into diner time.

4. better chance of getting home before dark in winter at Northern latitudes

Schools don't exist solely to prepare you for soul crushing work. It is supposed to actually educate you.

Working 9-to-5 is miserable. It only helps if the wolk you're doing is interesting.

For a child, school is usually not 'interesting'. Children shouldn't be subjected to misery.

P.s. Props to you for saying you're in the US, not just assuming it.

Because kids are too young to drink.

A lot of the school system is set on many of the people in the country being farmers so you do a lot of scheduling to allow them to work on the farm. This is why do you get the summers off and some other vacations that fit with other major times for growing crops?

I don't think school should emulate work.

Learning (well) isn't easy, attention spans are limited and after some time you get rapidly diminishing results.

I personally like the sound of inverting the structure we use for learning, meaning assigning the "theory" as homework and using class time to discuss or apply it afterwards.

At least that has the benefit of letting every student manage their time, spending more time on harder (for them) subjects.

The homework aspect in theory helps with the University structure.

To simulate modern work it should either be 8-6 with 30 minutes for lunch or a 0 hour contract where a different school calls you every day so you know which one to go to the next day, sometimes it’s 4am-12midday and sometimes 6pm-4am.

Instead of adopting the archaic 9-5, how about just eliminate homework?

Now I have been outa school since 2008, but back then, in public school, they didn't teach us shit. Like actual useful things. How to deal with emotions, personal finance, How to deal with police, mindfulness, critical thinking..nothing. all busy work and history through the American lense (propaganda). I even had a science teacher who was super religious and said earth was created 6000 years ago...it was geology ffs. Math was the worst imo. Solve for X, zero context. The only reasoning they gave to learn it was "to get in to college".

Safe to say I didn't go to college.

Ontario, Canada has all but eliminated homework entirely until high school. There is absolutely no good data saying it helps in acquisition or retention of skills over the long term. Completion of homework is also strongly correlated along class lines. If Suzy has a stable home, is fed well, and gets good sleep, she will likely have time and resources to complete homework. If Todd doesn’t, he likely won’t. We should focus on the in-school instruction. As far as the length of day? If you keep the kids longer it will cost more so it’s unlikely many jurisdictions will raise taxes for that expenditure.

When would the teachers have time to lesson plan or grade if they're teaching kids 8 hours a day?

It's interesting how different the quality of schooltime can be, and how perception of said time can differ for school kids as well. I was in a "full day" school starting from age 9 in a country where regular schools end at lunch time. Our school had the same curriculum to go through as every other, but lots more time to do it. The extra time was filled with dedicated self-learn time ( basically to do homework, but you have your classmates around to talk and help each other and can reach out to teachers if you really struggle with something) and elective extracurricular activities. It was mandatory, but you had free choice between all the offers. Teachers had to offer something, and usually offered their personal passion activities/hobbies. This led to these activities being the highlight of every kid's week, because there was enough variety to choose from to find something you liked. Kinda like club activities in US schools, but much less codified and without competitive objectives. Some examples are photography, pottery, soap box car building, school beautification ( we literally were allowed and encouraged to graffiti/mural the school walls :D ), gardening, natural science ( basically constantly doing fun physics and chemistry experiments without boring theory), electronics etc. . This was intentionally kept separate from sports or music, which also were partially elective: you had to do sports and music, and some basics were mandatory for all, but you could opt for specializations. All this semi-forced mingling served well to prevent the formation of strong clique boundaries, without inhibiting kids from pursuing their talents and passions.

All that had huge advantages. Kids from troubled families had a much easier time of keeping up with everyone else, as help from home was hardly necessary. Lunch was provided by the school. Wasn't stellar, wasn't horrible. But it was available to all students for free, and that can be very important to some as well. It took me a long time, often only after visiting school friends for the first time or even after schooltime was over entirely, to realize how crazy rich or poor some of my friends' families actually were, or what difficulties they sometimes faced at home and that there was a reason we never were invited to visit them. At school, it simply didn't matter to us. Sure, some wore more brand clothes than others, but nobody thought of using this as a measure of personal quality. Class cohesion also was usually strong. Sure, kids still were assholes and bullies like everywhere else, but it usually got solved internally quickly, because it was harder to keep it up for full days with plenty of "forced" social time, and you ended up being more confronted with the damage and hurt you caused. And in really bad cases the proximity to school made it much easier for teachers to pick up on any developments in their students and classes and react quickly. There also were some mandatory "social skill" classes to teach everyone basic conflict solving and mediating. It was only one or two sessions per year, but I think it actually helped, even if we kids usually scoffed at it at the time. It was very clear the school philosophy was not to push through a curriculum, but to use the extra time to help explore and form personalities that later will hopefully enmesh well in society. And yes, our school had a bit more teaching personnel than other schools to fill all the time slots and extra activities, but we still had 25-35 students per class, it was not some utopian dream.

We kids loved the full day spent at school as well. No homework, and what's better than spending the entire day with your friends? The school was far from my home, so I left the house at 6:30 and usually got back around 18:00, with about 40min of train commute plus 30min of walking (one way). Only Friday ended at lunch. Still never felt that I was lacking "me" time.

Tl;Dr : It matters a lot how the time at school is used.

I'm from Morocco, and school usually goes from 8 to 12, then again from 2 to 6, sometimes 3 to 7. Yes, we can leave school as late as 7 in the evening sometimes. During the winter, that's exactly when the sun sets. Also, you have lunch at home. Every. Single. Time. Also, only Wednesdays are exempt from afternoon school, but only if you're in primary school, because as soon as you enter secondary school, the whole week is filled up to the brim. And add homework on top of all this. And usually we get that from every single subject (yes, even PE). In many ways, this is worse than what you Muricans are doing. If you guys are being tortured, we're being sent to hell and back 5 days a week every single week for the most part. Also, 1 week holidays every 6 weeks. That's it. And since we're Muslims, we don't even get the 2-3 week "Christmas break". You stay home on January 1st, and go to school the very next day if it's not a weekend. We even study during Ramadan. It sucks less because we leave earlier, but it still sucks. Also, we don't have snow days. Only a super small part of the country gets snow, and you still have to go to school even if that happens. And during the final years of high school, you have a final exam that contains EVERY SINGLE LESSON IN THE YEAR. All of them. Both semesters. And you bet that I hated this when I had to go through it.

Schools in the US were designed to prepare kids for factory jobs initially. A lot of the structure related to that has changed but the amount of time you spend at school hasn't. Realistically you'd want a kid to spend less time at school. But schools are now used to prepare kids for working all day and then giving up their free time to their employer. That may be a little tin hat-ie, but it's at least partially true. However as a kid a few extra hours at school wouldn't have cut it for me. I preferred to do my work at home, I was also super distractible because I had adhd. Additionally as others have said that just wouldn't be feasible for a lot of kids/families.

My kids school in Sweden, at least age 6 to 12 have a school day from 8 till 13, or 14 for the older kids, and still no homework.

But long days would be counterproductive. Learning is hard work, that's part of the reason a new job is so exhausting. Doing that long hours for years would only burn kids out even more.

I think it's because there's some unwritten rule about not inducing children to commit suicide. I don't think a little kid could handle such a curriculum without getting severely depressed and offing themselves. Adult survival of this is much higher, mostly thanks to access to sex, drugs, and rock and roll, something children are not allowed to have access to, given local laws and their status as legal minors. It is correct to lie to them and make them think that if they are good students now they will be successful as adults because they are too young to be exposed to night clubs where 9 to fivers tend to find refuge and a drug dealer at the end of a tough shift to survive and avoid suicide.

If they had school until 5, when will the football team practice?

I'm not sure if adding more time in school would be helpful even if there's no homework. I have a 9-5 job, and by 3:30 I'm already mentally checked out for the day, just watching the ole clock tick slowly to five. Not to mention that kids aren't paid to go to school, so the kids wouldn't see any tangible benefits of a longer day. In theory they would learn more, but most kids aren't thinking that way and there's only so much a kid can learn in one day anyway.

I think we have homework because it’s cheap.

It would benefit the kids much more if they had extracurricular activities, clubs, and workshops after lecture classes, where they could actually apply what they learn during lectures.

But that would be expensive & hurt businesses bottom lines via increased taxation.

In the USA, work doesn't end at 5, and there's always homework. That's where your proposal goes wrong.

My daughter has ADHD and sitting through six hours of school is hard enough of her. Eight would give her ridiculous amounts of stress and anxiety. Sure, one day she'll have to build up to 8 hours when she gets a job, but she's got to build up to it. Now eliminating homework (except maybe reading literature), I'm all for that.

I've never understood homework. I didn't have any resonance with school work either. The whole endeavour seemed pointless until I needed to calculate the volume of loudspeaker cabinet or determine the voltage in a circuit. Only then the activity had any meaning and hence I was motivated to learn trigonometry or electromagnetic field theory. It wasn't even work because I love to learn. I failed almost every exam I ever attempted and yet meanwhile, back in reality, I was perfectly able to function and thrive in the technical world that we inhabit. Homework can eat my refuse.

I think there is some nefarious reasons for the current setup but here's a point I didn't see. People and children especially can't learn for 8 hours straight learning needs to be broken up with play time or eating or socializing. Then reinforcement of what you learned earlier before you go to sleep can be helpful. Ideally I don't think homework should be learning new subjects or really hard at all it should be a cake walk of whatever was learned during that day.

School in the US is designed to indoctrinate kids to be slaves.

While were at it, let's just remove school entirely. Children could compete in the free market of unpaid internships and develop skills that will be useful for their working life. I feel like government has had a monopoly on education for too long, let's let the free market do it's thing and save the day.