I designed a banner for a school which they want to print themselves instead of sending it to a printer. The file is very big, does anyone know how I can save it as multiple A3 pages so they sould be able to print it themselves?
Can you use the slice tool?
When I want to split a page in half or in 3 if I have to send a full spread to the printer in page parts, I go to the edit art board option and set the size of the page to what I need (in your case A3) slide the art board over the part of the spread that I want on that page and save it like that so that only what’s on the art board is saved. After I save I undo the art board changes and then save the next piece of the spread. Make sure to lock rulers where you want the slices before you start playing around with the art boards so that each piece matches up exactly and there are no gaps. It might be a concocted method but works for me! 
good luck!
kol hakavod you are even attempting to do the school’s request!! i would rather try and convince them to find a sponsor to print it professionally!!!
how about this article that shows you how to do it from a pdf?
Adobe PDF Tip: How To Print Large Posters Across Multiple Pages - NEXTOFWINDOWS.COM
Thanks for the article!
I would save the file as it is and then when it comes to printing there is a way to do it in the printing menu to split the document between pages