Where can I buy some radium water?

An x-ray device to see if the shoes fit correctly?

Leaded paint for my asbestos shingling?

Can I sell my vote for the next presidential election? (It used to be common!)

Hotel owners are forbidden from discriminating based on race. You want to allow it? Even if not perfect, it still works.

As someone without security clearance, I'm forbidden from a lot of places with secret information.

Even if there is still an underground market for elephant ivory in the US, forbidding its trade greatly reduced the demand.

Seems like on average forbidding things has been pretty effective.

In pretty much all countries that instituted heavy restrictions on smoking, e.g. banning smoking from restaurants, you can see an accelerated drop in number of smokers the years after that ban regardless of changes in education. This is particularly easy to verify because it has been done in many countries but all at fairly different points in time. Some did it decades ago, some have done it recently, there are still countries where it's allowed.

Forbidding things works very well most of the time. There are exceptions, but as a rule, it works.

Would a parent be allowed to send their kid in with a pack of smokes, and expect their kid can smoke them inside the school?

No?

Because it effects others and brings down the overall ability for the learning environment to succeed. Same deal with phones. If it makes the environment toxic to success, there should probably be some prohibition within those grounds. This isn't banning phones across the board, or banning them for kids. It's banning them within a location, like how firearms are banned inside courthouses.

Forbidding things works. People drank less during prohibition, and they do less drugs than they would were they legalized. Hence there is no serious proposal to legalize most hard drugs

Eh, nuance: forbidding things entirely, which people want to do, and don't really harm others, doesn't work.

Having separate spaces works a lot better. Which is why we have alcohol venue licensing. Forbidding kids from phones entirely, at the same time as adults are on them constantly, isn't going to work. But having a phone-free space like a smoke-free space is more viable.