In order to create a copy of the school letterhead, you will need to be logged in with a staff account. Copies will default to your personal Google Drive when made. You will need to move them and retitle them as appropriate.
We are now using Google Slides as our letterhead template. All templates are in one slide document. Once you make your copy, delete the slide templates you don't need. For two page documents, you will need to duplicate your selected template and edit the text boxes as appropriate.