Use views to prepopulate fields
If you don't want coding, this is one possibility:

If you only have one form, but hundreds of nodes, another way I would suggest to do it is to use Webform Template for the School content type. You can create one webform template and then reuse it for every school node, but the address field in the webform should have a default value that is a token of the node's address field. All you would need to do is set up your webform template's address field to have a default value of something like [node-field-school-address] and every instance of the webform will have the address of the node it belongs to. 

In order to use tokens in a webform, you will need this module: Webform Patched . This is a module that contains the Webform module itself along with token support an therefore the original Webform module should be disabled. I implemented this myself for my site and it worked without any problems. 

I never worked with addressfield, but I found this module in case you need it: Addressfield tokens