Can schools see every website you visit, messenger text messages, apps you download, etc

My school claimed that they can see all of our messages, photos sent and etc. As long as we're on their campus wi-fi. Is this true or only a bluff? And what if your using your own device, such as an iphone and are just using their Wi-Fi? Now if it is true, can they track the specific device? And owner? Or do they only have the ability to block that specific device. I would assume that they would get the device information, but if its a school with thousands of kids how would they pinpoint the student? Would using a VPN change anything? Lastly, would spoofing your mac address prevent tracking (if possible) or do anything at all?

Yes they can

This is actually not true. It's just a statement too scare the children from doing anything inappropriate online on school grounds. And yes, they have the ability too block some websites (YouTube, ect.) but nothing that isn't bad.

Yes, it's quite normal now. A government organisation (especially an educational organisation) has a minimum legal obligation to accurately audit and store any internet communication.

VPN should be blocked by any competent organisation where there's a policy to control access. There will be a clear policy not to circumvent security policies that means you'll be kicked out when discovered.

I don't see what you mean about MAC spoofing or any relevance.

They can 100% see what web sites you visit, and may be able to see some of the contents, other stuff will be encrypted, which means they can only see you are accessing xyz.com, not what you are viewing.

Assume messaging apps can be monitored.

Files downloaded can certainly be logged.

A VPN make you stick out like a sore thumb. They can't see the contents, but they can see you are using a VPN, and most schools simply block VPN traffic by default.

Changing your Mac address? That just makes it appear like you are using a different network card. It's still your log in details that are associated with the mac and IP address.

Look these filters where designed by people that know a LOT more about computer networks that you do. Trying to bypass them is just going to get you noticed, and you computer access removed.
But you need it for your course work? Tough luck.

Yes!

Yes, they can see and monitor any device on their network, that is their right and they actually have to to ensure your safety and check you are not doing anything illegal as its them that is responsible. As for seeing every message or photo you send, this all depends on the setup, if it is a standard network, as long as your connection to say facebook or website is HTTPS then no they can't. But this is not foolproof, if they are really serious they can actually intercept this traffic too and read and look at it, this is not too common just check the agreement you signed up for when you agreed to using it. As for telling who you are, if its a phone they can ask for your details if you do something illegal but most PCs they would just block.