From when is it possible to register a change of address?

First purchase a mailbox and then form a mailbox family.

But for that, you first need an address, right?
For example, we still don't know a house number that we will get.
I’m not familiar with the formalities about when you can apply for a house number.

I believe we received them relatively soon after the start of construction. But that was already well over 2 years ago, so I can't remember exactly. I just checked on the Dresden homepage, and the building permit and the site plan are definitely required for the application.

Have you ever been there in person? Our neighbor also registered his son at school half a year earlier, but drove 18 km each way every day.

Yes, we both also work nearby (about 4 km away). But the guest school application was just rejected - despite the note about the start of construction, etc.

But first you need an address, right? For example, we don't know the house number yet, which we will eventually get. I don't know the formalities about when you can apply for a house number.

We already have a house number - some houses are already standing there. And I think it's also stated in the purchase contract.

I would also first seek a personal conversation with the school at the construction site. In our case, after consulting with the municipality and the school, neighbors were also able to register their child at the future place of residence for the school, even though they were still building at the start of the school year. However, they had to accept the longer daily trips. The neighbors who are building now will do the same, and the registration also seemed to work relatively smoothly there.

I would also first try to have a personal conversation with the school at the construction site. In our case, after consulting with the municipality and the school, neighbors were able to register their child at the future place of residence for the school, even though they were still building at the start of the school year. They just had to accept the longer daily trips. The neighbors who are building now will do the same, and registration apparently worked relatively smoothly there as well.

Within one municipality? We are moving from municipality A to municipality B and the mayor of A absolutely does not want to release our child because the municipality invested a few million in renovating the school(s) last year and this year. The school in municipality B would gladly take our child - we have already had talks. They cannot understand it at all. At the moment, the only option left is the sledgehammer approach – moving into any random apartment in municipality B before school starts. But we actually wanted to avoid that. It costs a ton of money and nerves. Just to move again a few months later.

Then your child really moves in with grandma - before you rent an apartment!? No guest room/office or anything like that available? The child doesn't have to sleep there, no one will check...