To download the school district number for a list of accounts go to the mail merge screen in reports.
Create a query of the accounts that you want to get their school district number. Click on View Records.
Go to the options menu and click on Download School District Numbers. It will now go thru the list and add an Additional Info called School District in each account. If there is already a different school district by the account it will change the old one to Old School District.
Update - 8/13/15
Added the state of Minnesota.